fix(hooks): pre-commit hook warns instead of failing on flush error

Fixes GH#483 - The pre-commit hook was blocking commits when
`bd sync --flush-only` failed, even if the user had removed beads
from their branch. This made it impossible to commit on branches
that don't have beads configured.

Changes:
- Change "Error:" to "Warning:" in the message
- Remove `exit 1` so commits proceed even if flush fails
- Add comments explaining why we don't block commits

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

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

examples/git-hooks/pre-commit

@@ -1,5 +1,5 @@
 #!/bin/sh
-# bd-hooks-version: 0.22.2
+# bd-hooks-version: 0.29.0
 #
 # bd (beads) pre-commit hook
 #
@@ -46,10 +46,12 @@ 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 "Error: Failed to flush bd changes to JSONL" >&2
+    echo "Warning: Failed to flush bd changes to JSONL" >&2
     echo "Run 'bd sync --flush-only' manually to diagnose" >&2
-    exit 1
+    # 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)