[B2c] Show project stats in TUI sidebar

[four-bytes-robby]

Purpose

Display live project stats (files indexed, chunks, memories, KB entries) in the brain TUI sidebar.

Design

1. Add getProjectStats() function in src/status.ts (or new src/stats.ts):

   • Query DB for: document count, chunk count, memory count, KB entry count
   • Cache for 30s (no need to re-query on every status update)

2. Extend BrainStatusEvent payload in src/status.ts:

   • Add optional stats field: { documents: number, chunks: number, memories: number, kbEntries: number }

3. Extend BrainStatusBar in src/tui.tsx:

   • Sidebar variant: add third row below progress bar showing compact stats
   • Format: 📄 142 files · 🧩 847 chunks · 🧠 23 memories · 📚 5 KB
   • Only show when stats available and state is "ready"

Acceptance

• Project stats visible in TUI sidebar when brain is ready
• Counts update after ingest completes
• No flicker (30s cache)
• Tests: stats computation, TUI rendering with stats

[coderabbitai]

🔗 Related PRs

#140 - fix: reduce throttle to 0.5s, fix sidebar layout wrapping [merged]
#141 - fix: session-scoped status + full width sidebar [merged]
#148 - fix: sidebar always subscribes to brain/status for ingest progress [merged]
#155 - feat: project-scoped bus + immediate auto-ingest + app.log warnings #151 #152 #153 [merged]
#171 - fix: wire HTTP polling fallback for brain TUI status #170 [merged]

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