chore: track Nx 22 AI tooling artefacts injected by generators

Nx 22 generators inject AI agent tooling into the repo via marked
sections and side files. Rather than re-deleting them after every
generator run, track the workspace-level ones and document why.

- CLAUDE.md gains a 'General Guidelines for working with Nx' section
  between Nx-managed markers; future Nx versions will update this
  section automatically without touching our project rules above.
  Pre-existing prettier-formatted blank lines added before code blocks
  are kept.
- .claude/settings.json (228 bytes) enables the nx-claude-plugins
  marketplace from nrwl/nx-ai-agents-config; tracked for contributor
  consistency. The personal .claude/settings.local.json stays
  gitignored.
- .github/ is the Nx AI skills/prompts/agents catalog. Kept despite
  being GitHub-named; it does not conflict with our Gitea workflows
  which will live under .gitea/workflows/ (per ADR-0015).
- .gitignore picks up Nx-managed transient dirs (.nx/polygraph,
  .claude/worktrees) and a trailing newline fix.

AGENTS.md is removed: it duplicated only the Nx auto-injected guidance
that CLAUDE.md already carries (CLAUDE.md is the strictly broader file
- project rules + Nx section). One source of truth for AI-agent
guidance.

.github/skills/nx-import/references/TURBOREPO.md

@@ -0,0 +1,62 @@
+## Turborepo
+
+- Nx replaces Turborepo task orchestration, but a clean migration requires handling Turborepo's config packages.
+- Migration guide: https://nx.dev/docs/guides/adopting-nx/from-turborepo#easy-automated-migration-example
+- Since Nx replaces Turborepo, all turbo config files and config packages become dead code and should be removed.
+
+## The Config-as-Package Pattern
+
+Turborepo monorepos ship with internal workspace packages that share configuration:
+
+- **`@repo/typescript-config`** (or similar) — tsconfig files (`base.json`, `nextjs.json`, `react-library.json`, etc.)
+- **`@repo/eslint-config`** (or similar) — ESLint config files and all ESLint plugin dependencies
+
+These are not code libraries. They distribute config via Node module resolution (e.g., `"extends": "@repo/typescript-config/nextjs.json"`). This is the **default** Turborepo pattern — expect it in virtually every Turborepo import. Package names vary — check `package.json` files to identify the actual names.
+
+## Check for Root Config Files First
+
+**Before doing any config merging, check whether the destination workspace uses shared root configuration.** This decides how to handle the config packages.
+
+- If the workspace has a root `tsconfig.base.json` and/or root `eslint.config.mjs` that projects extend, merge the config packages into these root configs (see steps below).
+- If the workspace does NOT have root config files — each project manages its own configuration independently (similar to Turborepo). In this case, **do not create root config files or merge into them**. Just remove turbo-specific parts (`turbo.json`, `eslint-plugin-turbo`) and leave the config packages in place, or ask the user how they want to handle them.
+
+If unclear, check for the presence of `tsconfig.base.json` at the root or ask the user.
+
+## Merging TypeScript Config (Only When Root tsconfig.base.json Exists)
+
+The config package contains a hierarchy of tsconfig files. Each project extends one via package name.
+
+1. **Read the config package** — trace the full inheritance chain (e.g., `nextjs.json` extends `base.json`).
+2. **Update root `tsconfig.base.json`** — absorb `compilerOptions` from the base config. Add Nx `paths` for cross-project imports (Turborepo doesn't use path aliases, Nx relies on them).
+3. **Update each project's `tsconfig.json`**:
+   - Change `"extends"` from `"@repo/typescript-config/<variant>.json"` to the relative path to root `tsconfig.base.json`.
+   - Inline variant-specific overrides from the intermediate config (e.g., Next.js: `"module": "ESNext"`, `"moduleResolution": "Bundler"`, `"jsx": "preserve"`, `"noEmit": true`; React library: `"jsx": "react-jsx"`).
+   - Preserve project-specific settings (`outDir`, `include`, `exclude`, etc.).
+4. **Delete the config package** and remove it from all `devDependencies`.
+
+## Merging ESLint Config (Only When Root eslint.config Exists)
+
+The config package centralizes ESLint plugin dependencies and exports composable flat configs.
+
+1. **Read the config package** — identify exported configs, plugin dependencies, and inheritance.
+2. **Update root `eslint.config.mjs`** — absorb base rules (JS recommended, TypeScript-ESLint, Prettier, etc.). Drop `eslint-plugin-turbo`.
+3. **Update each project's `eslint.config.mjs`** — switch from importing `@repo/eslint-config/<variant>` to extending the root config, adding framework-specific plugins inline.
+4. **Move ESLint plugin dependencies** from the config package to root `devDependencies`.
+5. If `@nx/eslint` plugin is configured with inferred targets, remove `"lint"` scripts from project `package.json` files.
+6. **Delete the config package** and remove it from all `devDependencies`.
+
+## General Cleanup
+
+- Remove turbo-specific dependencies: `turbo`, `eslint-plugin-turbo`.
+- Delete all `turbo.json` files (root and per-package).
+- Run workspace validation (`nx run-many -t build lint test typecheck`) to confirm nothing broke.
+
+## Key Pitfalls
+
+- **Trace the full inheritance chain** before inlining — check what each variant inherits from the base.
+- **Module resolution changes** — from Node package resolution (`@repo/...`) to relative paths (`../../tsconfig.base.json`).
+- **ESLint configs are JavaScript, not JSON** — handle JS imports, array spreading, and plugin objects when merging.
+
+Helpful docs:
+
+- https://nx.dev/docs/guides/adopting-nx/from-turborepo