GL-339: Rewrite docs/architecture.md + reconcile 'no raw SQL' doctrine + repo hygiene

[discodone]

Review source

Round 14 (Gemini + Opus 4.8) — P2/P3, dangerously misleading docs.

Problem

1. docs/architecture.md is completely out of date — it describes a simple Python script, not the layered FastAPI application that exists. A new developer would be completely lost.
2. CLAUDE.md states 'No raw SQL anywhere' yet raw SQL with ?/text() placeholders lives in auth/auth.py (workspace resolver), api_keys.py, exports.py, challenges.py, health.py. The architecture doc contradicts reality.
3. Repo hygiene: stray '=0.19.0' file (a pip install redirection artifact), coverage.json, scripts/output.log, logs/ are all uncommitted clutter in the tree.
4. License inconsistency: README.md states 'Apache License 2.0' while the license badge points to MIT.

Fix

• Rewrite docs/architecture.md from scratch: FastAPI, Routers, Services, Repositories, arq workers, SQLAlchemy, multi-tenancy model. Use a request-flow diagram through the layers.
• Reconcile the 'no raw SQL' claim: either remove the absolute claim from CLAUDE.md and document where/why raw SQL is used (with parameterization safety notes), or migrate the remaining raw SQL to ORM
• Clean repo: rm the '=0.19.0' artifact, add coverage.json, scripts/output.log, logs/ to .gitignore
• Fix license inconsistency: align README, badge, and LICENSE file

Acceptance Criteria

• architecture.md accurately reflects the current layered design
• CLAUDE.md no longer contradicts reality re: raw SQL
• .gitignore covers all build/log artifacts; junk files removed
• License is consistent across README, badge, LICENSE
• mypy clean, ruff clean, tests >= baseline