-feat: add self-hosted Docker image (roadmap)

[InlitX]

Implements the roadmap item "Self-hosted Docker image".

• Dockerfile: multi-stage build, serves SPA + 45+ API handlers on port 3000.
• docker-compose.yml: one service, optional env file for API keys.
• Sidecar: LOCAL_API_MODE=standalone serves dist/ and listens on 0.0.0.0; static serving uses path.relative() to prevent path traversal.
• README: Option 4 (Self-hosted Docker) and platform table updated; roadmap checkbox done.
• CHANGELOG: entry under [Unreleased].

Desktop (Tauri) unchanged; standalone is opt-in via env. node --test src-tauri/sidecar/local-api-server.test.mjs — all 8 tests pass.

[vercel]

@InlitX is attempting to deploy a commit to the eliehabib projects Team on Vercel.

A member of the Team first needs to authorize it.

[SebastienMelki]

Thanks for working on this @InlitX — self-hosted Docker has been on the roadmap for a while, good to see someone tackling it.

Couple of things I'd like to understand better:

1. Image size — what's the final image size after the multi-stage build? Curious if there's room to slim it down (alpine base, etc.).
2. Path traversal fix — you mention path.relative() to prevent traversal. Could you share more about how that's validated? Want to make sure the static serving is locked down properly.
3. Health check — is there a health endpoint or readiness probe for orchestrators (k8s, docker-compose health checks)?

The 8 passing tests are great. Will review the code in detail soon.