docs(setup): version aliases.zsh + gitconfig.txt under docs/setup/dotfiles

80-dotfiles.sh was reading notes/aliases.zsh and notes/gitconfig.txt,
but notes/ is gitignored - fresh clones on the dev VM hit "file not
found" and the script aborted.

Move both templates to docs/setup/dotfiles/ where they ship with every
clone. gitconfig.txt's [user] block now carries placeholder identity
(your name / your.email@example.com) instead of the original author's
identity - the script overlays the prompted values at install time so
the file content doesn't matter functionally, but the placeholders
read more clearly as "fill me in".

80-dotfiles.sh source paths flipped from $REPO_ROOT/notes/... to
$REPO_ROOT/docs/setup/dotfiles/.... Step-3 table row, §8.4 (dotfiles
repo appendix), and the setup README index updated accordingly. New
"dotfiles/" section in the setup README documents the folder.

The notes/aliases.zsh and notes/gitconfig.txt on existing dev
workstations are unaffected - those files live outside the repo and
this PR doesn't touch them.

docs/setup/scripts/80-dotfiles.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
-# Wire up the project-specific dotfiles:
-#   - symlink notes/aliases.zsh → ~/.oh-my-zsh/custom/aliases.zsh
-#   - copy notes/gitconfig.txt to ~/.gitconfig and overlay your identity
+# Wire up the project-wide dotfiles:
+#   - symlink docs/setup/dotfiles/aliases.zsh → ~/.oh-my-zsh/custom/aliases.zsh
+#   - copy docs/setup/dotfiles/gitconfig.txt to ~/.gitconfig and overlay your identity
 set -euo pipefail
 # shellcheck source=./lib.sh
 source "$(cd "$(dirname "$0")" && pwd)/lib.sh"
@@ -14,8 +14,10 @@ if [[ -z "$REPO_ROOT" ]]; then
   exit 1
 fi
 
+DOTFILES_DIR="$REPO_ROOT/docs/setup/dotfiles"
+
 # ─── 1. Aliases ───────────────────────────────────────────────────────
-SOURCE_ALIASES="$REPO_ROOT/notes/aliases.zsh"
+SOURCE_ALIASES="$DOTFILES_DIR/aliases.zsh"
 if [[ ! -f "$SOURCE_ALIASES" ]]; then
   err "$SOURCE_ALIASES not found."
   exit 1
@@ -42,7 +44,7 @@ else
 fi
 
 # ─── 2. gitconfig — copy + identity overlay ───────────────────────────
-SOURCE_GITCONFIG="$REPO_ROOT/notes/gitconfig.txt"
+SOURCE_GITCONFIG="$DOTFILES_DIR/gitconfig.txt"
 if [[ ! -f "$SOURCE_GITCONFIG" ]]; then
   err "$SOURCE_GITCONFIG not found."
   exit 1