Make the repo self-hostable: root-default image, one-command compose, deploy docs

[asymetryk]

Continues the "anybody can deploy this repo" initiative (follows PR #3). Covers deployability slices 2, 3, 5, and 7.

Changes

• Image serves at root by default (slice 3). Dockerfile no longer bakes BASE_PATH=/observatory; it defaults BASE_PATH/SOURCE_REVISION to root/dev and re-declares the build args in the runtime stage. Deploy under a subpath with --build-arg BASE_PATH=/observatory (as the operator's K3s UAT does).
• One-command self-host (slice 2). docker-compose.yml gains a web service that builds the image and serves the demo app at http://localhost:3000 with a health check. Postgres moves behind an optional db profile, since the app runs in demo mode and only drizzle-kit needs the database.
• Self-host deploy guide (slice 5). New DEPLOY.md (demo mode, Compose, plain Docker at root/subpath, local Node, Cloudflare, env-var reference). README.md now leads with a one-command self-host and a local-first MCP endpoint, keeping the homelab URL only as a labeled aside.
• K3s manifests labeled operator-reference (slice 7). New deployment/README.md + a header note make clear the Tailscale/K3s manifests are the maintainer's homelab setup, not a generic target.

Verification

pnpm lint, pnpm typecheck, pnpm test all pass (25 tests). Because no Docker daemon is available in the agent VM, I validated the image path directly instead:

• Production build succeeds at root (BASE_PATH="").
• The exact standalone runtime the image runs (node apps/web/server.js, with .next/static + public copied as the Dockerfile does) serves / → 200, /api/health → {"ok":true,...}, and the compose healthcheck command exits 0. Static assets (CSS) resolve (200).
• Base-path routing verified both ways: default server → /=200, /api/health=200; BASE_PATH=/observatory server → /=404, /observatory=200, /observatory/api/health=200.

Root (production standalone image) and subpath both render fully styled:

Production image serving the app at root

Same app served under /observatory via BASE_PATH

Note

Docker Compose itself couldn't be run end-to-end here (no Docker daemon in the Cloud Agent VM), but every layer it depends on (image build, runtime CMD, health endpoint, base path) is verified above.

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