Add documentation and implementation report

IMPLEMENTATION_REPORT.md

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+# Implementation Report
+
+## Built
+
+Implemented the live in-lecture quiz portal per `SPEC.md`: FastAPI backend, SQLite schema with WAL, signed student and admin cookies, quiz pool validation, modular scoring, student/admin APIs, WebSocket state machine, auto-close, CSV export, vanilla student/admin frontends, example Week 9 question pool, docs, and tests.
+
+File inventory and line counts:
+
+```text
+app/: 1400 lines
+static/: 775 lines
+tests/: 504 lines
+examples/week9_pool.json: 127 lines
+total across app, static, tests, examples: 2806 lines
+```
+
+## Test Results
+
+`pytest -q`:
+
+```text
+31 passed, 33 warnings in 5.43s
+```
+
+`pytest --cov=app`:
+
+```text
+31 passed, 33 warnings in 5.48s
+TOTAL 854 statements, 67 missed, 92.15% coverage
+Required test coverage of 80.0% reached.
+```
+
+Smoke test:
+
+```text
+uvicorn app.main:app started successfully on 127.0.0.1:8001
+GET /healthz returned {"ok":true,"version":"0.1.0","sessions_active":0,"ws_clients":0}
+```
+
+## Run Locally
+
+```bash
+python3 -m venv .venv
+. .venv/bin/activate
+pip install -e '.[dev]'
+cp .env.example .env
+uvicorn app.main:app --host 127.0.0.1 --port 8001 --reload
+```
+
+## Deviations and Notes
+
+- Server-side QR SVG data URLs are used instead of a client-side QR library.
+- `live_histogram` is pushed on every accepted submission, not throttled.
+- Broadcast sends are queued so slow WebSocket clients do not block state changes.
+- `static/observer.html` is a placeholder because the observer page is optional.
+- FastAPI emits a non-fatal `on_event` deprecation warning with the installed package version.
+
+## Open Issues
+
+No known functional blockers. The admin UI is intentionally plain and should be reviewed with the instructor workflow in mind before classroom use.
+
+## Review Carefully
+
+- The late-join behavior and missed-submission rows.
+- The session control flow from `lobby` through `finished`.
+- CSV shape against the exact spreadsheet format wanted for class records.
+- The generated example questions, because they are plausible placeholders.