docs(setup): use ~/.bashrc hand-off instead of chsh for zsh switch

chsh is blocked on the corp dev VM (PAM-level restriction at user-
provisioning time). Drop the sudo chsh -s call from 20-zsh.sh and
append a guarded `exec zsh -l` block to ~/.bashrc instead — same UX
without needing infra escalation, also matches the legacy WSL setup
pattern in 02-wsl-terminal-setup.md.

The hand-off is guarded by `case $- in *i*)` so non-interactive bash
flows (scp, rsync, cron) are unaffected, and by a ZSH_VERSION absence
check to prevent re-exec loops.

Main doc and README table descriptions updated to match.

docs/setup/01-dev-debian-vm-setup.md

@@ -161,9 +161,9 @@ The `bootstrap.sh` script runs every numbered script (`10-…` → `80-…`) in
 What each script does:
 
 | Script                                               | Effect                                                                                                                                                                                                                       | Idempotent? |
-| ---------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------- |
+| ---------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------- |
 | [`10-base-packages.sh`](scripts/10-base-packages.sh) | `apt update` + install base packages (curl wget git build-essential ca-certificates gnupg software-properties-common)                                                                                                        | ✅          |
-| [`20-zsh.sh`](scripts/20-zsh.sh)                     | Install zsh, set as default shell. Install Oh My Zsh, Powerlevel10k, plugins (autosuggestions, syntax-highlighting). Patch `~/.zshrc`.                                                             | ✅          |
+| [`20-zsh.sh`](scripts/20-zsh.sh)                     | Install zsh + Oh My Zsh + Powerlevel10k + plugins (autosuggestions, syntax-highlighting). Patch `~/.zshrc` (theme + plugins + fzf hook) and `~/.bashrc` (exec zsh on interactive shells — `chsh` is blocked on the corp VM). | ✅          |
 | [`30-cli-tools.sh`](scripts/30-cli-tools.sh)         | Install `bat eza fd-find ripgrep fzf zoxide ncdu keychain` + `jq yq httpie make tree htop tmux direnv dnsutils unzip`. Aliases for the Debian-renamed binaries (`batcat`→`bat`, `fdfind`→`fd`).                              | ✅          |
 | [`40-node.sh`](scripts/40-node.sh)                   | Install nvm. Install Node from the repo's `.nvmrc` (currently `24`). Enable corepack, pin pnpm to `package.json`'s `packageManager`.                                                                                         | ✅          |
 | [`50-docker.sh`](scripts/50-docker.sh)               | Install Docker CE + compose plugin from the Docker apt repo. Add the current user to the `docker` group. Enable `docker.service`.                                                                                            | ✅          |

docs/setup/README.md

@@ -14,11 +14,11 @@ Step-by-step setup procedures for new contributors. Each file is self-contained
 Modular setup scripts called from the doc above. Each is idempotent, each can be re-run safely. Run via the orchestrator (`bootstrap.sh`) or individually.
 
 | Script                                               | Purpose                                                                                                                                                                          |
-| ---------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------- |
+| ---------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
 | [`bootstrap.sh`](scripts/bootstrap.sh)               | Run every numbered script in order with a confirmation prompt at each step.                                                                                                      |
 | [`lib.sh`](scripts/lib.sh)                           | Common helpers — colour logging, idempotent `apt_install` / `ensure_line`.                                                                                                       |
 | [`10-base-packages.sh`](scripts/10-base-packages.sh) | apt + base packages every other script assumes (`curl wget git build-essential …`).                                                                                              |
-| [`20-zsh.sh`](scripts/20-zsh.sh)                     | zsh, Oh My Zsh, Powerlevel10k, autosuggestions, syntax-highlighting. Patches `~/.zshrc`.                                                 |
+| [`20-zsh.sh`](scripts/20-zsh.sh)                     | zsh + Oh My Zsh + Powerlevel10k + autosuggestions + syntax-highlighting. Patches `~/.zshrc` (theme / plugins / fzf hook) and `~/.bashrc` (exec zsh — `chsh` blocked on corp VM). |
 | [`30-cli-tools.sh`](scripts/30-cli-tools.sh)         | `bat eza fd-find ripgrep fzf zoxide ncdu keychain` + dev extras (`jq yq httpie make tree htop tmux direnv`).                                                                     |
 | [`40-node.sh`](scripts/40-node.sh)                   | nvm + Node from the repo's `.nvmrc` + corepack pinned to `package.json#packageManager`'s pnpm version.                                                                           |
 | [`50-docker.sh`](scripts/50-docker.sh)               | Docker CE + compose plugin from docker.com apt repo + user added to `docker` group + service enabled at boot.                                                                    |

docs/setup/scripts/20-zsh.sh

@@ -9,15 +9,33 @@ require_not_root
 
 apt_install zsh
 
-# Make zsh the default shell for $USER (idempotent).
+# Hand off to zsh from ~/.bashrc rather than `chsh -s`. The corp infra
-current_shell="$(getent passwd "$USER" | cut -d: -f7)"
+# locks the default shell at user-provisioning time and `chsh` is denied
-zsh_path="$(command -v zsh)"
+# (the standard PAM-level restriction). The .bashrc hand-off achieves
-if [[ "$current_shell" != "$zsh_path" ]]; then
+# the same UX without needing infra escalation, and it's compatible with
-  log "Setting zsh as default shell for $USER (sudo will prompt)."
+# both interactive SSH sessions and VSCode Remote-SSH's bash bootstrap.
-  sudo chsh -s "$zsh_path" "$USER"
+BASHRC="$HOME/.bashrc"
-  ok "Default shell set to $zsh_path. Takes effect on next login."
+[[ -f "$BASHRC" ]] || touch "$BASHRC"
+MARKER='# Managed by docs/setup/scripts/20-zsh.sh — apf-portal zsh hand-off.'
+
+if grep -qF "$MARKER" "$BASHRC"; then
+  skip "zsh hand-off already in $BASHRC."
 else
-  skip "zsh already default shell."
+  cat >> "$BASHRC" <<'EOF'
+
+# Managed by docs/setup/scripts/20-zsh.sh — apf-portal zsh hand-off.
+# Hand off to zsh on interactive shells. The `case $-` guard avoids
+# breaking non-interactive bash (scp, rsync, cron, …), and the
+# ZSH_VERSION check prevents an infinite re-exec loop.
+case $- in
+  *i*)
+    if command -v zsh >/dev/null 2>&1 && [ -z "${ZSH_VERSION-}" ]; then
+      exec zsh -l
+    fi
+    ;;
+esac
+EOF
+  ok "Patched $BASHRC to exec zsh on interactive shells."
 fi
 
 # Oh My Zsh — install with RUNZSH=no to avoid spawning zsh during the script.