[FEATURE] Status bar widget — ZeroDB memory count and sync state

[urbantech]

Summary

• Adds statusline/zerodb-status.sh — a lightweight status bar widget for Claude Code that shows ZeroDB memory state without hitting the API on every poll
• Registers the script in .claude-plugin/plugin.json via the new statusline field
• Updates hooks/session-end.sh to write a saving state to the cache immediately before persist runs
• Updates hooks/session-start.sh to write a synced state to the cache after recall completes

How it works

The statusline script reads from a local cache file (${TMPDIR:-/tmp}/zerodb-status/status.json) written by the session hooks. This avoids API calls on every status bar poll. Display states:

ZeroDB: 24 memories ✓   # synced with count
ZeroDB: saving...        # session-end hook is running
ZeroDB: 0 memories       # synced, no memories yet
ZeroDB: offline          # error state
ZeroDB: ready            # no cache yet (first session)

If ZERODB_API_KEY is not set, the script exits 0 silently so the status bar shows nothing.

Test Plan

• Set ZERODB_API_KEY and verify status bar renders ZeroDB: ready on first run
• After a session with memories, confirm ZeroDB: N memories ✓ displays
• Confirm ZeroDB: saving... appears briefly during session-end hook execution
• Unset ZERODB_API_KEY and confirm status bar shows nothing (no clutter)
• Manually write error state to cache and verify ZeroDB: offline renders

Risk/Rollback

Low risk — additive only. The statusline script is read-only and cache-based. Hooks write a small JSON file to /tmp; no API calls, no side effects on existing session behavior. Rollback: remove statusline field from plugin.json.

Closes #11