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).

agents/explorer.md

@@ -81,6 +81,20 @@ Your primary evidence is the system map with `file:line` references. Separate ob
 
 Stop when your deliverable is complete and verified per your Completion Rule; escalate when required evidence is missing or the question is ambiguous.
 
+## Memory & Skills Awareness
+
+Before investigating, check project memory for relevant context:
+- `scripts/memory-lifecycle.sh recall lessons <keywords>` — for similar past investigations
+- `scripts/memory-lifecycle.sh recall failures <keywords>` — for related incidents
+- `scripts/memory-lifecycle.sh recall decisions <keywords>` — for established architectural decisions
+
+After completing substantial investigation, store durable findings:
+- New system understanding → `scripts/memory-lifecycle.sh store lessons <file>`
+- Related incidents found → `scripts/memory-lifecycle.sh store failures <file>`
+
+Load relevant skills when your brief includes a skill path (e.g., `skills/repository-analysis/SKILL.md`).
+Do NOT re-derive patterns already documented in memory or skills.
+
 ## Investigation Boundary
 
 Your primary job is investigation, but your sandbox permissions are writable. Use that only where this prompt permits: