feat: add skills, memory, delegation and self-learning (Phase 3)

Add three Hermes-inspired capabilities to Shira:

- Skills system: firm-wide workflow templates (list/view/manage tools),
  4 pre-seeded skills (case summary, hearing prep, direct access report,
  deadline tracker), auto-learning via post-conversation meta-prompt
- Cross-conversation memory: per-lawyer profiles and per-case memory
  stored as bounded markdown files, injected into system prompts
- Sub-agent delegation: spawn up to 3 child AgentRunner instances for
  parallel document analysis and complex multi-step tasks

New files: skills.py, memory.py, delegate.py, learner.py, 4 SKILL.md
Updated: agent_runner (6 new tools, depth/blocked_tools support),
prompt_builder (skills/memory injection), route (memory loading,
background learning), main.py (data dirs), Dockerfile (pyyaml, skills)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pyproject.toml

@@ -10,6 +10,7 @@ dependencies = [
     "pydantic>=2.10.0",
     "mcp>=1.0.0",
     "openai>=1.50.0",
+    "pyyaml>=6.0",
 ]
 
 [project.optional-dependencies]