feat: multi-worktree watch and daemon support

[tinker495]

Summary

Split from #109 (4/4). Adds worktree-aware daemon PID management and multi-worktree parallel watching. Includes PR 3 commits (feat/worktree-detection) - merge PR 3 first.

• Worktree-specific PID/ready/log files in daemon package
• discoverWorktreesForWatch() for automatic linked worktree detection with auto-init
• watchProject() extracted for single-project watch loop
• Multi-worktree parallel watching via errgroup
• Platform-specific liveness detection (pipe on Unix, poll on Windows)
• Bug fix: Lock file handle leak in WriteWorktreePIDFile (defer close after lock)
• Bug fix: Deduplicate no-worktree path to use watchProject() instead of inline copy
• Bug fix: Remove duplicate doc comment on watchProject

Test plan

• go build ./... passes (linux, windows, darwin)
• go vet ./... clean
• go test ./daemon/... ./cli/... all pass with -race
• Updated existing watch tests for new signatures

Merge order: PR 3 (#114) → this PR

Part of #109 split. See also: PR 1 (#112), PR 2 (#113), PR 3 (#114, dependency)

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 31.28079% with 279 lines in your changes missing coverage. Please review.
✅ Project coverage is 35.67%. Comparing base (a322537) to head (afa2aac).
⚠️ Report is 62 commits behind head on main.

Files with missing lines	Patch %	Lines
cli/watch.go	18.21%	228 Missing and 1 partial ⚠️
daemon/daemon.go	57.69%	34 Missing and 10 partials ⚠️
daemon/daemon_unix.go	80.00%	3 Missing and 1 partial ⚠️
daemon/workspace.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #115      +/-   ##
==========================================
+ Coverage   27.16%   35.67%   +8.51%     
==========================================
  Files          32       42      +10     
  Lines        3711     6755    +3044     
==========================================
+ Hits         1008     2410    +1402     
- Misses       2620     4136    +1516     
- Partials       83      209     +126     

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[yoanbernabeu]

Review & Testing Summary ✅

Full local testing completed — everything looks great.

Tests performed

1. Backward compatibility (PR binary on main-indexed project)

• search on existing index: identical results and scores ✅
• watch --status / watch --stop / watch --background: all work correctly ✅
• init --yes on a new project: behavior unchanged ✅
• Existing .grepai/ directory (config.yaml, index.gob, symbols.gob) read without issues ✅

2. New worktree features

• Auto-init via search: running grepai search in a linked worktree with no .grepai/ auto-creates it by copying config + index + symbols from main worktree. Search works immediately. ✅
• init --inherit: correctly detects worktree, displays info (main worktree path, worktree ID, backend), inherits config, warns about GOB per-worktree isolation. ✅
• Multi-worktree watch: from main worktree, discovers 2 linked worktrees, watches all 3 projects in parallel via errgroup. ✅
• Incremental indexing: file added in a worktree during watch is detected, indexed (1 chunk), and symbols extracted. Subsequent search returns it as top result. ✅

3. Unit tests

• make test (go test -v -race ./...): all pass, 0 failures ✅

Action needed

There's a merge conflict with main — please rebase/merge to resolve it, then we can merge.

gh pr checkout 115 && git fetch origin main && git merge origin/main

[tinker495]

Follow-up: merged latest upstream main as well (commit afa2aac) and resolved the only merge conflict in config/config_worktree_test.go.\n\nRe-validation:\n- go test ./... (all passing locally)\n\nCurrent PR merge state is no longer DIRTY (now UNSTABLE while checks update).

[yoanbernabeu]

Great work! 🎉

Conflict resolved, all CI checks green, code reviewed — merging.