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*

skills/README.md

@@ -0,0 +1,35 @@
+# Skills
+
+Skills are learned procedures that Hope distills from conversations.
+One `.md` file per skill, saved here by the skills MCP server
+(`agent/skills_mcp.py`) and mounted into the container at `/skills`.
+
+## How they differ from memory
+
+- **Memory** (`./memory/`) stores *facts*: names, preferences, things
+  Hope should remember.
+- **Skills** (this directory) store *how to do things*: repeatable
+  procedures, workflows, and multi-step tasks Hope has learned.
+
+## File format
+
+```markdown
+# Make a Coffee Order
+
+How to place an order at the local coffee shop on behalf of the user.
+
+## Steps
+1. Confirm the usual drink (oat latte, extra hot).
+2. Ask if they want anything new today.
+3. Read back the order and confirm.
+4. Tell them the pickup time.
+
+---
+Created: 2026-08-22T12:00:00+00:00
+Source: conversation-learned
+```
+
+Hope saves a skill when it successfully completes a multi-step task or
+the user teaches it a new procedure, and recalls one with `skill_recall`
+before performing a task it has done before. Skills are updated in place
+when the procedure improves.