Phase 1-3: Add memory, skills, and improvement systems

- memory/: cross-session project memory with decisions, lessons, failures,
  architecture, and sessions categories. Each has format templates and
  lifecycle documentation.
- skills/: 12 reusable specialized methodologies (tdd, systematic-debugging,
  architecture-design, code-review, security-review, repository-analysis,
  failure-analysis, refactoring, test-analysis, incident-investigation,
  browser-automation, research). Each has frontmatter and methodology sections.
- improvements/: proposal-based improvement system requiring human approval.
- scripts/memory-lifecycle.sh: deterministic memory operations (recall, store,
  list, search, sessions, cleanup).
- scripts/test-memory-system.sh: 12 structural tests for all new systems.
- orchestrator.md: added Memory Recall stage, Learning and Memory Storage
  stage, Improvement Proposals workflow, memory/skills rules, and 3 new
  actions (A23-A27) to the action catalog. Updated behavioral acceptance test
  and state separation model.
- All 12 subagents: added Memory & Skills Awareness sections with recall
  and store instructions.
- docs/AGENT_ARCHITECTURE.md: documented memory, skills, and improvements
  systems (sections 12-14). Updated action count (27), state model, and
  remaining weaknesses.
- README.md: documented new systems, updated repository layout, added
  test-memory-system.sh documentation.

All 39 tests pass (16 architecture + 12 memory + 11 bootstrap).

memory/sessions/README.md

@@ -0,0 +1,57 @@
+# Session State
+
+Cross-session continuity for long-running work.
+
+## Purpose
+
+When OpenCode restarts, the system needs to know:
+- What was being worked on
+- What was completed
+- What was interrupted
+- What the next step should be
+
+## Format
+
+```markdown
+# Session-NNNN: <task summary>
+
+Started: YYYY-MM-DD HH:MM
+Last updated: YYYY-MM-DD HH:MM
+Status: active | interrupted | completed
+
+## Task
+
+<what was being done>
+
+## Completed
+
+<what was finished>
+
+## In Progress
+
+<what was interrupted>
+
+## Next Steps
+
+<what should happen next>
+
+## Context
+
+<relevant facts needed to resume — decisions, evidence, file paths>
+```
+
+## Lifecycle
+
+- Session records are created at the start of significant work
+- Updated incrementally as work progresses
+- Marked `completed` when the task is done
+- Left as `interrupted` if the session ends mid-task
+- Old sessions (>7 days, completed) can be archived or removed
+
+## Recovery
+
+On session restart, the Orchestrator:
+1. Checks `memory/sessions/` for `active` or `interrupted` sessions
+2. Reads the context from the most recent relevant session
+3. Decides whether to resume or start fresh
+4. Creates a new session record if starting fresh