T-1: initialize monorepo structure with backend and frontend scaffolds

Backend: Spring Boot 3.5.11 on Java 25, Maven with wrapper, hexagonal
architecture package layout (domain/application/adapter/config), health
endpoint with integration test. Originally planned for Spring Boot 4.0
but pivoted due to massive package reorganization in 4.0 (see addenda
in research and plan docs).

Frontend: Vue 3 scaffolded via create-vue with TypeScript, Vue Router,
Vitest, ESLint, Prettier. Pivoted from Svelte due to ecosystem maturity
concerns (broken router ecosystem for Svelte 5).

Also: extended .gitignore for Java/Maven and Node/Vue artifacts, updated
CLAUDE.md with tech stack, build commands, agent documentation sections,
and document integrity rule.

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

CLAUDE.md

@@ -20,6 +20,7 @@ These are the non-negotiable principles of this project. Every decision — arch
 - Always write tests before implementation (TDD). Red → Green → Refactor.
 - Refactoring is permitted freely as long as it does not alter the fundamental architecture.
 - No vibe coding. Every line of code must be intentional and traceable to a requirement.
+- Document integrity: when a decision is revised (pivot), add an addendum with rationale — never rewrite or delete the original decision. Traceability over tidiness.
 
 ### Privacy
 
@@ -54,6 +55,33 @@ These are the non-negotiable principles of this project. Every decision — arch
 - A docker-compose example in the README is sufficient.
 - Documentation lives in the README. No wiki, no elaborate docs site.
 
+### Tech Stack
+
+- **Backend:** Java 25 (LTS, installed via SDKMAN), Spring Boot 3.5.x, Maven with wrapper (`./mvnw`)
+- **Frontend:** Vue 3, TypeScript, Vue Router, Vite, Vitest, ESLint, Prettier
+- **Node.js:** 24 LTS (for Docker/CI; development tolerates newer versions)
+- **Base package:** `de.fete`, hexagonal architecture (single Maven module, package-level separation)
+- **No Pinia** — Composition API (`ref`/`reactive`) + localStorage is sufficient
+- **No JPA until T-4** — added when database infrastructure is ready
+
+### Build Commands
+
+| What | Command |
+|------|---------|
+| Backend test | `cd backend && ./mvnw test` |
+| Backend run | `cd backend && ./mvnw spring-boot:run` |
+| Frontend install | `cd frontend && npm install` |
+| Frontend build | `cd frontend && npm run build` |
+| Frontend test | `cd frontend && npm run test:unit` |
+| Frontend dev | `cd frontend && npm run dev` |
+
+### Agent Documentation
+
+- Research reports: `docs/agents/research/`
+- Implementation plans: `docs/agents/plan/`
+- Agent test reports (browser verification): `.agent-tests/` (gitignored)
+- Use the `browser-interactive-testing` skill (rodney/showboat) for visual verification — this is an agent tool, not manual work.
+
 ### Ralph Loops
 
 - Autonomous work is done via Ralph Loops. See [.claude/rules/ralph-loops.md](.claude/rules/ralph-loops.md) for documentation.