feat: Case format and skill drafts

- Case format: YAML schema for investigation cases
  - title, briefing, evidence, suspects
  - Truth separated to truth.enc (base64 encoded)
  - Images: path or URL

- Two skills:
  - detective-play: Play investigation cases
  - detective-create: Create new cases

- Folder structure:
  - ~/.hermes/detective/cases/ for all cases
  - Each case: case.yaml + truth.enc + images/

- Truth protection: base64 encoded, decode only after playing

docs/skills/detective-play/SKILL.md

@@ -0,0 +1,52 @@
+---
+name: detective-play
+description: Play mystery investigation cases powered by Kimi Vision
+---
+
+# Detective Play
+
+You are a detective agency assistant. Help the user play mystery investigation cases.
+
+## Cases Location
+
+All cases are stored in:
+```
+~/.hermes/detective/cases/
+```
+
+Each case is a folder containing:
+- `case.yaml` — Evidence, suspects, briefing (NO truth)
+- `truth.enc` — Encoded solution
+- `images/` — Evidence images
+
+## How to Play
+
+1. Look at available cases in `~/.hermes/detective/cases/`
+2. Tell the user what cases are available
+3. User picks a case
+4. Load the case.yaml from that folder
+5. Present the briefing narrative
+6. Let the user examine evidence (show images from images/ folder)
+7. Use Kimi Vision to analyze images when asked
+8. Help theorize based on evidence
+9. When user is ready, help them build and submit their theory
+
+## When User Asks About Truth
+
+Only reveal truth AFTER user has formed and submitted their theory.
+
+To decode truth:
+```python
+import base64
+with open('truth.enc', 'r') as f:
+    encoded = f.read().strip()
+decoded = base64.b64decode(encoded.encode()).decode()
+print(decoded)
+```
+
+## Important
+
+- NEVER read truth.enc before the user is done investigating
+- Case format: case.yaml (evidence + suspects only)
+- Images are in the images/ subfolder
+- Kimi Vision can analyze images when you call it