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- Shims are never marked as "outdated"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/post-checkout

@@ -1,89 +1,16 @@
 #!/bin/sh
-# bd-hooks-version: 0.30.7
+# bd-shim v1
 #
-# bd (beads) post-checkout hook
+# bd (beads) post-checkout hook - thin shim
 #
-# This hook syncs the bd database after a branch checkout:
-# 1. Checks if any .beads/*.jsonl file was updated
-# 2. Runs 'bd sync --import-only --no-git-history' to import changes
-#
-# Arguments provided by git:
-# $1 = ref of previous HEAD
-# $2 = ref of new HEAD
-# $3 = flag (1 if branch checkout, 0 if file checkout)
-#
-# Install: cp examples/git-hooks/post-checkout .git/hooks/post-checkout && chmod +x .git/hooks/post-checkout
-
-# Only run on branch checkouts
-if [ "$3" != "1" ]; then
-    exit 0
-fi
-
-# Skip during rebase - git checks out commits during rebase and we must not
-# modify working tree files (like deletions.jsonl) or the rebase will fail
-if [ -d .git/rebase-merge ] || [ -d .git/rebase-apply ]; then
-    exit 0
-fi
+# This shim delegates to 'bd hooks run post-checkout' 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
+    # Silently skip - post-checkout is called frequently
     exit 0
 fi
 
-# Check if we're in a bd workspace
-if [ ! -d .beads ]; then
-    exit 0
-fi
-
-# Detect git worktree: compare --git-dir and --git-common-dir
-GIT_DIR=$(git rev-parse --git-dir 2>/dev/null)
-GIT_COMMON_DIR=$(git rev-parse --git-common-dir 2>/dev/null)
-if [ -n "$GIT_DIR" ] && [ -n "$GIT_COMMON_DIR" ]; then
-    GIT_DIR_ABS=$(cd "$GIT_DIR" 2>/dev/null && pwd || echo "$GIT_DIR")
-    GIT_COMMON_DIR_ABS=$(cd "$GIT_COMMON_DIR" 2>/dev/null && pwd || echo "$GIT_COMMON_DIR")
-    
-    if [ "$GIT_DIR_ABS" != "$GIT_COMMON_DIR_ABS" ]; then
-        # We're in a git worktree
-        cat >&2 <<'EOF'
-
-╔══════════════════════════════════════════════════════════════════════════╗
-║ Welcome to beads in git worktree!                                        ║
-╠══════════════════════════════════════════════════════════════════════════╣
-║ Note: Daemon mode is not recommended with git worktrees.                 ║
-║ Worktrees share the same database, and the daemon may commit changes     ║
-║ to the wrong branch.                                                      ║
-║                                                                          ║
-║ RECOMMENDED: Disable daemon for this session:                            ║
-║   export BEADS_NO_DAEMON=1                                               ║
-║                                                                          ║
-║ For more information:                                                     ║
-║   - Run: bd doctor                                                        ║
-║   - Read: docs/GIT_INTEGRATION.md (lines 10-53)                          ║
-║                                                                          ║
-║ Issue tracking: bd-dc9                                                    ║
-╚══════════════════════════════════════════════════════════════════════════╝
-
-EOF
-    fi
-fi
-
-# Check if any JSONL file exists in .beads/
-if ! ls .beads/*.jsonl >/dev/null 2>&1; then
-    exit 0
-fi
-
-# Run bd sync --import-only --no-git-history to import the updated JSONL
-# --no-git-history prevents writes to deletions.jsonl (critical during rebase)
-if ! output=$(bd sync --import-only --no-git-history 2>&1); then
-    echo "Warning: Failed to sync bd changes after checkout" >&2
-    echo "$output" >&2
-    echo "" >&2
-    echo "Run 'bd doctor --fix' to diagnose and repair" >&2
-    # Don't fail the checkout, just warn
-fi
-
-# Run quick health check (silent on success, hints if issues found)
-# This catches version mismatches, outdated hooks, etc.
-bd doctor --check-health 2>/dev/null || true
-
-exit 0
+exec bd hooks run post-checkout "$@"