feat(install-targets): add claude-project (per-project Claude Code) adapter

Completes the install-target matrix for Claude Code. Until now, ECC's
Claude support was home-scope only (~/.claude/) via the `claude` target.
This adds a project-scope counterpart (./.claude/) via a new
`claude-project` target so teams can install ECC per-repo without
contaminating ~/.claude/ — matching the existing project-scope adapters
for Cursor, Antigravity, Gemini, CodeBuddy, Joycode, and Zed.

Symmetric with `claude`:
- Same namespace under rules/ecc and skills/ecc
- Same docs/<locale> handling for --locale
- Same hooks placeholder substitution for hooks.json
- Reuses claude-home's destination-mapping logic 1:1

Use cases:
- Monorepos with multiple Flow-managed projects
- Teams that want ECC scoped per-project without touching ~/.claude/
- Per-project skill/rule isolation when global install isn't desirable

No breaking change: existing --target claude continues to route to
claude-home (user-scope) unchanged. New target is opt-in.

Tests
-----
- 4 new tests in tests/lib/install-targets.test.js
  (root resolution, lookup-by-id, plan parity with claude, foreign-path filtering)
- All install-target regression guards (schema enum / SUPPORTED_INSTALL_TARGETS)
  still pass
- End-to-end smoke: `--target claude-project --profile minimal --dry-run`
  emits 359 ops with destinations rooted at <projectRoot>/.claude/ (parity
  with --target claude which emits 359 ops rooted at ~/.claude/)

scripts/lib/install/request.js

@@ -100,8 +100,8 @@ function normalizeInstallRequest(options = {}) {
       `Unsupported locale: "${locale}". Supported locales: ${listSupportedLocales().join(', ')}`
     );
   }
-  if (locale && target !== 'claude') {
-    throw new Error('--locale can only be used with --target claude');
+  if (locale && target !== 'claude' && target !== 'claude-project') {
+    throw new Error('--locale can only be used with --target claude or --target claude-project');
   }
   const requestedIncludeComponentIds = dedupeStrings([
     ...(config?.includeComponentIds || []),