Add Phase 23c self-hosting steps and replace fixed test count invariant

Adds 6 steps (482-487) for architect/worker dispatch: step spec expander,
convention extractor+validator, prior-step context injector, worker
dispatch protocol, test plan generator with 9-type taxonomy, and
integration proof. Replaces "12 tests per step" invariant with
complexity-driven test planning.

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

ARCHITECT.md

@@ -70,7 +70,7 @@ experienced engineers think about projects before implementation begins.
 
 - **Header-only C++** — all implementation in .h files, no .cpp (except mcp_main.cpp and test files)
 - **600-line file limit** — split when approaching, use Extended/Impl pattern
-- **12 tests per step, 8 for integration** — consistent test density
+- **Test plans generated per-step from complexity analysis** — test count and type emerge from what's being built (unit, negative, integration, contract, boundary, property, smoke, performance, regression), not from a fixed template. Architect approves the plan before workers execute. Prior sprints used a fixed "12 tests per step" scaffold; Sprint 23c replaces this with the test plan generator.
 - **MCP-first** — every capability exposed as an MCP tool
 - **Headless-first** — all functionality works without GUI
 - **No external dependencies beyond tree-sitter** — regex parsers for languages without tree-sitter grammars