feat: context compaction + skills system

Compaction:
- GemmaLLM.chat() truncates ChatContext to last 30 items (~15 turns)
  before sending to LLM, preventing context window overflow on long
  conversations. Preserves system prompt and removes orphaned tool calls.

Skills:
- agent/skills_mcp.py: MCP server with skill_save, skill_recall,
  skill_list, skill_update tools backed by .md files in /skills
- skills/ dir bind-mounted into container, git-trackable
- System prompt instructs Hope to save repeatable procedures as skills
  and recall them before performing tasks she's done before
- Distinct from memory (facts) — skills are learned *procedures*

docker-compose.yml

@@ -19,6 +19,7 @@ services:
       - ./livekit.yaml:/etc/livekit.yaml:ro
       - ./certs:/etc/voice/certs
       - ./memory:/memory
+      - ./skills:/skills
     healthcheck:
       test: ["CMD-SHELL", "curl -sk https://localhost:8090/ -o /dev/null && curl -s http://localhost:7880/ -o /dev/null"]
       interval: 15s