feat(web): add web UI and Coolify compose deployment

`ghglance -serve :8080` runs a web UI from the same binary: submit a
username, a background job renders every card in every theme, and
/u/<user> shows them again with a theme picker and embed URLs.

- Cards are stored on disk with atomic symlink publishing and deleted
  after -retention (default 24h); -cooldown limits token-less regeneration.
- Token-less jobs use a public-only server token with private and org
  scope forced off; a submitter's own token is used for that job only and
  never stored or logged. The form links to GitHub's new-token page with
  the needed scopes pre-ticked.
- The CLI and web share one fetch helper; CLI output is unchanged.
- compose.yml deploys to Coolify with a data volume and /healthz check.

.dockerignore

@@ -0,0 +1,12 @@
+# The image needs only go.mod, main.go, internal/ and entrypoint.sh. Keep
+# secrets and local output out of the Docker context and its cached layers.
+.env
+*.env
+data/
+output/
+.git
+.github
+.claude
+plans/
+demo/
+docs/