docs: implement issues 0013 and 0014 — LESSONS.md and docs/spec/

Add LESSONS.md as the long-loop feedback log at repo root. Patterns
observed during development graduate to standing rules when three or
more entries appear.

Introduce docs/spec/ as the living spec layer: overview.md (deployed
state) and architecture.md (directory structure, install pipeline,
provider model, governance layer). Refactor docs/VISION.md to goals
and intent only — architecture content moved to docs/spec/architecture.md.

Update CLAUDE.md and CONTEXT.md to reference the new spec files.
Close issues 0013 and 0014. Update ROADMAP and factory integration
note to reflect completion.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

LESSONS.md

@@ -0,0 +1,9 @@
+# Lessons
+
+Patterns observed during development of this repo. Three or more entries on the same pattern → promote to CONTEXT.md (or the relevant instruction file) as a standing rule.
+
+**Graduation rule:** When three or more entries cover the same pattern, the human reviews and promotes it to the appropriate standing location: `CONTEXT.md` for domain-level principles, `core/instructions/coding.md` for coding conventions, `core/instructions/git.md` for git conventions, or `core/instructions/testing.md` for testing conventions. The graduated entries are marked `[graduated → target file]` rather than deleted (audit trail).
+
+**Who writes here:** The session-handoff skill (Chunk 3) prompts LESSONS.md extraction before closing a session. The human may also write directly.
+
+**What belongs here:** Non-obvious observations — a rule that was misapplied, a pattern that caused friction, a decision that turned out wrong in practice. Not summaries of what was built (that's git history) or planned changes (that's issues).