docs: PRD v1.2 — Wursor rename, key decisions locked, all gaps addressed

- Renamed product from Wordbench to Wursor across all touchpoints
- Locked key decisions: Electron + Code-OSS shell, Claude BYO key, wp-env only v1
- Added first-run experience (§7.1.8), error states (§8.5), agent substrate (§8.1.1)
- Expanded State Diff lifecycle (§6.4), Knowledge Graph strategy (§6.2)
- Strengthened verify-as-proof principle (§5, §7.1.6)
- Added metrics baselines + owners (§11), exit criteria for Phases 1-2 (§12)
- Added test strategy (§C.1), accessibility/i18n as non-goal (§C)
- Created IMPLEMENTATION.md — TDD-driven 8-sprint build guide

README.md

@@ -1,4 +1,4 @@
-# Wordbench
+# Wursor
 
 **Working title.** Agentic WordPress development environment — code, live site, WP-CLI, and shipping in one loop.
 
@@ -7,7 +7,8 @@
 ## Start here
 
 - Full product spec: [PRD.md](./PRD.md)
+- Build guide (TDD, sprints, CI): [IMPLEMENTATION.md](./IMPLEMENTATION.md)
 
 ## Status
 
-Spec / Phase 0. Implementation has not started.
+Spec / Phase 0. Implementation has not started.