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/label.md

@@ -0,0 +1,33 @@
+---
+description: Manage issue labels
+argument-hint: [command] [issue-id] [label]
+---
+
+Manage labels on beads issues. Labels provide flexible cross-cutting metadata beyond structured fields (status, priority, type).
+
+## Available Commands
+
+- **add**: Add a label to an issue
+  - $1: "add"
+  - $2: Issue ID
+  - $3: Label name
+
+- **remove**: Remove a label from an issue
+  - $1: "remove"
+  - $2: Issue ID
+  - $3: Label name
+
+- **list**: List labels on a specific issue
+  - $1: "list"
+  - $2: Issue ID
+
+- **list-all**: Show all labels used across all issues
+
+## Common Label Use Cases
+
+- Technical scope: `backend`, `frontend`, `api`, `database`
+- Quality gates: `needs-review`, `needs-tests`, `security-review`
+- Effort sizing: `quick-win`, `complex`, `spike`
+- Context: `technical-debt`, `documentation`, `performance`
+
+Use `bd label add <issue-id> <label>` to tag issues with contextual metadata.