docs: docker-compose example + self-hosting guide

[buremba]

Summary

Closes the documentation gap that surfaced in #766. Adds:

• docker-compose.example.yml at repo root — copy, generate two secrets, docker compose up -d, done.
• docs/DOCKER.md — what's actually required at boot vs nice-to-have, boot-error troubleshooting, provider story, production checklist.
• .env.example rewritten — drops the misleading "CLAUDE CONFIGURATION (Required)" header, replaces it with a clear "Required to boot" section listing only DATABASE_URL, ENCRYPTION_KEY, BETTER_AUTH_SECRET. All LLM provider keys explicitly marked optional.

Why now

External user (#766) tried to docker-compose up against ghcr.io/lobu-ai/lobu-app and hit {"level":"error","msg":"Failed to start server","error":{}} — empty error. PR #843 fixed the empty-error logging. This commit fills the remaining gap: they should not have needed to debug a server error to find out that ENCRYPTION_KEY exists. Now they don't.

Notable corrections

The old .env.example claimed ANTHROPIC_API_KEY was "Required" — it's not. The server boots fine without any provider keys, and per-provider keys can be added at runtime via the admin UI. Reality (verified by reading packages/server/src/server.ts:main()):

Var	Required?
DATABASE_URL	yes, explicit throw
ENCRYPTION_KEY	yes, secrets in DB can't decrypt without it
BETTER_AUTH_SECRET	yes for Docker/k8s (ephemeral default only in lobu run local CLI mode)
ANTHROPIC_API_KEY / OPENAI_API_KEY / etc.	no

Test plan

• Sample compose validates with docker compose -f docker-compose.example.yml config.
• Smoke test: cp the example, generate the two secrets, docker compose up -d, open localhost:8787, sign in. (Untested locally — flagging so a reviewer or follow-up can confirm before sharing the file externally.)
• .env.example still parseable as .env (no syntax surprises).

Refs #766.

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📥 Commits

Reviewing files that changed from the base of the PR and between 16998ab and fa27610.

📒 Files selected for processing (3)

• .env.example
• docker-compose.example.yml
• docs/DOCKER.md

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/docker-quickstart

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