docs: add canonical IA landing + first-pass core pages

docs/06-configuration.md

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+# Configuration
+
+This page documents how Mission Control is configured across local dev, self-host, and production.
+
+## Config sources (first pass)
+
+- Docker Compose uses `compose.yml` plus environment variables.
+- Backend reads env vars (see `backend/app/core/config.py`).
+- Frontend uses Next.js env vars at build/runtime (see `frontend/` plus `compose.yml`).
+
+## Key environment variables
+
+### Frontend
+- `NEXT_PUBLIC_API_URL` — backend base URL reachable from the browser
+- `NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY` — enables Clerk in the frontend when set
+
+### Backend
+- `DATABASE_URL` — Postgres connection string
+- `CORS_ORIGINS` — comma-separated allowed origins
+- `CLERK_JWKS_URL` — enables Clerk JWT verification on protected routes
+- `DB_AUTO_MIGRATE` — whether to auto-run migrations on startup (see backend docs/config)
+
+## Secrets handling
+- Do not commit secret keys.
+- Prefer `.env` files that are excluded by `.gitignore`.
+
+## Links
+- Deployment notes: [docs/deployment/README.md](deployment/README.md)
+- Production notes: [docs/production/README.md](production/README.md)