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/reopen.md

@@ -0,0 +1,22 @@
+---
+description: Reopen closed issues
+argument-hint: [issue-ids...] [--reason]
+---
+
+Reopen one or more closed issues.
+
+Sets status to 'open' and clears the closed_at timestamp. Emits a Reopened event.
+
+## Usage
+
+- **Reopen single**: `bd reopen bd-42`
+- **Reopen multiple**: `bd reopen bd-42 bd-43 bd-44`
+- **With reason**: `bd reopen bd-42 --reason "Found regression"`
+
+More explicit than `bd update --status open` - specifically designed for reopening workflow.
+
+Common reasons for reopening:
+- Regression found
+- Requirements changed
+- Incomplete implementation
+- New information discovered