Add command documentation and improve daemon UX

- Added human-readable uptime formatting (51m 59s vs 3119.4 seconds)
- Fixed daemon stop race condition with SIGKILL
- Added markdown docs for 19 commands: blocked, comments, compact, daemon,
  delete, dep, epic, export, import, label, list, quickstart, rename-prefix,
  renumber, reopen, repos, restore, stale, sync
- Closed: bd-159, bd-152, bd-168
- Deleted test issues: bd-144, bd-145

Amp-Thread-ID: https://ampcode.com/threads/T-9f7c3fed-62de-4bcd-a059-8c1b77cdb841
Co-authored-by: Amp <amp@ampcode.com>

commands/sync.md

@@ -0,0 +1,28 @@
+---
+description: Synchronize issues with git remote
+argument-hint: [--dry-run] [--message]
+---
+
+Synchronize issues with git remote in a single operation.
+
+## Sync Steps
+
+1. Export pending changes to JSONL
+2. Commit changes to git
+3. Pull from remote (with conflict resolution)
+4. Import updated JSONL
+5. Push local commits to remote
+
+Wraps the entire git-based sync workflow for multi-device use.
+
+## Usage
+
+- **Basic sync**: `bd sync`
+- **Preview**: `bd sync --dry-run`
+- **Custom message**: `bd sync --message "Closed sprint issues"`
+- **Pull only**: `bd sync --no-push`
+- **Push only**: `bd sync --no-pull`
+
+## Note
+
+Most users should rely on the daemon's automatic sync (`bd daemon --auto-commit --auto-push`) instead of running manual sync. This command is useful for one-off syncs or when not using the daemon.