feat(hooks): implement thin shim pattern (GH#615)

Replace full shell script hooks with thin shims that delegate to
'bd hooks run <hook-name>'. This eliminates hook version drift -
upgrading bd automatically updates hook behavior.

Changes:
- Add 'bd hooks run' subcommand with hook logic in Go
- Convert templates to minimal shims (~17 lines each)
- Shims use '# bd-shim v1' marker (format version, not bd version)
- Update version checking to recognize shim format
- Shims are never marked as "outdated"

Benefits:
- No more manual 'bd hooks install --force' after upgrades
- Hook logic always matches installed bd version
- Follows pattern used by husky, pre-commit, lefthook

Migration: Run 'bd hooks install --force' one final time.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/templates/hooks/pre-commit

@@ -1,63 +1,18 @@
 #!/bin/sh
-# bd-hooks-version: 0.30.7
+# bd-shim v1
 #
-# bd (beads) pre-commit hook
+# bd (beads) pre-commit hook - thin shim
 #
-# This hook ensures that any pending bd issue changes are flushed to
-# .beads/issues.jsonl before the commit is created, preventing the
-# race condition where daemon auto-flush fires after the commit.
-#
-# When sync-branch is configured in config.yaml, .beads changes are committed
-# to a separate branch via worktree, so auto-staging is skipped.
-#
-# Installation:
-#   cp examples/git-hooks/pre-commit .git/hooks/pre-commit
-#   chmod +x .git/hooks/pre-commit
-#
-# Or use the install script:
-#   examples/git-hooks/install.sh
+# This shim delegates to 'bd hooks run pre-commit' which contains
+# the actual hook logic. This pattern ensures hook behavior is always
+# in sync with the installed bd version - no manual updates needed.
 
 # Check if bd is available
 if ! command -v bd >/dev/null 2>&1; then
-    echo "Warning: bd command not found, skipping pre-commit flush" >&2
+    echo "Warning: bd command not found in PATH, skipping pre-commit hook" >&2
+    echo "  Install bd: brew install steveyegge/tap/bd" >&2
+    echo "  Or add bd to your PATH" >&2
     exit 0
 fi
 
-# Check if we're in a bd workspace
-if [ ! -d .beads ]; then
-    # Not a bd workspace, nothing to do
-    exit 0
-fi
-
-# Check if sync-branch is configured in config.yaml or env var
-# If so, .beads changes go to a separate branch via worktree, not the current branch
-SYNC_BRANCH="${BEADS_SYNC_BRANCH:-}"
-if [ -z "$SYNC_BRANCH" ] && [ -f .beads/config.yaml ]; then
-    # Extract sync-branch value from YAML (handles quoted and unquoted values)
-    # Use head -1 to only take first match if file is malformed
-    SYNC_BRANCH=$(grep -E '^sync-branch:' .beads/config.yaml 2>/dev/null | head -1 | sed 's/^sync-branch:[[:space:]]*//' | sed 's/^["'"'"']//' | sed 's/["'"'"']$//')
-fi
-if [ -n "$SYNC_BRANCH" ]; then
-    # sync-branch is configured, skip flush and auto-staging
-    # Changes are synced to the separate branch via 'bd sync'
-    exit 0
-fi
-
-# Flush pending changes to JSONL
-# Use --flush-only to skip git operations (we're already in a git hook)
-# Suppress output unless there's an error
-# Note: We warn but don't fail - this allows commits to proceed even if
-# beads has issues (e.g., user removed .beads from their branch)
-if ! bd sync --flush-only >/dev/null 2>&1; then
-    echo "Warning: Failed to flush bd changes to JSONL" >&2
-    echo "Run 'bd sync --flush-only' manually to diagnose" >&2
-    # Don't block the commit - user may have removed beads or have other issues
-fi
-
-# Stage all tracked JSONL files (beads.jsonl, issues.jsonl for backward compat, deletions.jsonl for deletion propagation)
-# git add is harmless if file doesn't exist
-for f in .beads/beads.jsonl .beads/issues.jsonl .beads/deletions.jsonl; do
-    [ -f "$f" ] && git add "$f" 2>/dev/null || true
-done
-
-exit 0
+exec bd hooks run pre-commit "$@"