feat: add diagnostic web app shell

.planning/phases/007-web-app-shell-diagnostic-start/007-CONTEXT.md

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+# Phase 7 Context: Web App Shell and Diagnostic Start
+
+**Status:** Ready for execution
+**Started:** 2026-04-26
+
+## Goal
+
+Serve the first browser UI from the Go backend and let a job seeker start
+diagnostic practice without API tooling.
+
+## Requirements
+
+- WEB-01: User can open a web app served by the Go service.
+- WEB-02: User can create a diagnostic interview session from the web app.
+- WEB-03: User can answer a diagnostic question and see rubric feedback.
+
+## UX Direction
+
+Visual thesis: quiet interview coaching workspace, dense but readable, with one
+clear green accent for action and readiness.
+
+Content plan:
+
+- left rail: learner setup
+- main workspace: active diagnostic questions and answer input
+- right context: grading feedback and evidence
+
+Interaction thesis:
+
+- loading states on API actions
+- inline error region
+- selected question state and answer result refresh
+
+## Out of Scope
+
+- Full progress view.
+- Material/ontology workspace.
+- Authentication.

.planning/phases/007-web-app-shell-diagnostic-start/007-PLAN.md

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+# Phase 7 Plan: Web App Shell and Diagnostic Start
+
+**Status:** Ready for execution
+**Phase Goal:** Create a working diagnostic web app shell.
+
+## Tasks
+
+### 1. Serve embedded web app
+
+- Add `internal/webapp`.
+- Embed static app assets.
+- Register root and asset routes through the existing Go server.
+
+### 2. Build diagnostic UI
+
+- Add setup form for user id, target role, stack, and interview timeline.
+- Create diagnostic session through the real API.
+- Show returned questions.
+
+### 3. Build answer and grading UI
+
+- Let user select a question.
+- Submit answer through the real API.
+- Show overall grade, scores, follow-up, and evidence.
+
+### 4. Verify
+
+- Add HTTP tests for root web app and asset serving.
+- Run Go tests, OpenSpec validation, line-count check.
+- Smoke the rendered app endpoint and diagnostic API flow.
+
+## Out of Scope
+
+- Frontend build tooling.
+- Authentication.
+- Phase 8 progress panels.

.planning/phases/007-web-app-shell-diagnostic-start/007-RESEARCH.md

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+# Phase 7 Research: Web App Shell and Diagnostic Start
+
+## Findings
+
+The existing Go backend can serve static assets without adding frontend build
+tooling. For the first MVP UI, plain HTML/CSS/JavaScript is enough and keeps
+the repo dependency-light.
+
+The diagnostic APIs already provide all Phase 7 data:
+
+- `POST /api/v1/diagnostic-sessions`
+- `POST /api/v1/diagnostic-sessions/{id}/answers`
+- `GET /api/v1/diagnostic-sessions/{id}`
+
+## Recommended Shape
+
+- Add `internal/webapp` with embedded static assets.
+- Register web app routes from `httpapi.Handler`.
+- Keep frontend files small and focused.
+- Use fetch calls directly against existing API routes.
+
+## Risks
+
+- A mock UI would not prove the backend loop. The UI must call real APIs.
+- A marketing-style landing page would distract from the core product surface.
+- Overbuilding a frontend stack before interaction validation would violate
+  YAGNI.

.planning/phases/007-web-app-shell-diagnostic-start/007-SUMMARY.md

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+# Phase 7 Summary
+
+**Status:** Complete
+**Completed:** 2026-04-26
+
+## Delivered
+
+- Added embedded web app serving from the Go backend.
+- Added `GET /` app shell and `/assets/*` static asset handling.
+- Built dependency-light HTML/CSS/JavaScript UI for diagnostic practice.
+- Added setup form for user id, target role, stack, and timeline.
+- Added real API-backed diagnostic session creation.
+- Added question selection, answer submission, and rubric feedback rendering.
+- Added loading, error, empty, and selected-question states.
+- Added web app route and asset tests.
+
+## Verification
+
+```powershell
+gofmt -w cmd internal
+go test ./...
+openspec validate frontend-mvp --strict
+openspec validate bootstrap-job-tutor-platform --strict
+```
+
+Additional smoke check:
+
+- `GET /` returned the app shell.
+- `GET /assets/app.js` returned the browser script.
+- Diagnostic session creation and answer grading succeeded through the same
+  server used by the app.
+
+## Deferred
+
+- Progress panels for memory/readiness/next challenge.
+- Material and asset workspace.
+- Browser screenshot audit.

.planning/phases/007-web-app-shell-diagnostic-start/007-VERIFICATION.md

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+# Phase 7 Verification
+
+## Verdict
+
+PASS
+
+## Requirement Coverage
+
+- WEB-01: PASS. The Go service serves the web app at `/`.
+- WEB-02: PASS. The browser app can create diagnostic sessions through the real
+  backend API.
+- WEB-03: PASS. The browser app can submit answers and render typed rubric
+  feedback, scores, follow-up, and evidence.
+
+## Evidence
+
+- `go test ./...` passed.
+- `openspec validate frontend-mvp --strict` passed.
+- `openspec validate bootstrap-job-tutor-platform --strict` passed.
+- Live root/asset HTTP smoke passed.
+- Live diagnostic create/answer smoke passed through the same server.
+
+## Residual Risk
+
+The UI was verified with HTTP/API smoke but not yet with a browser screenshot
+audit. Phase 8 should add browser-backed checks once the progress view is
+included.