feat: F5.6b server F as an image: the editor from F itself, one stack per environment

F hands out the editor's page and bundle (editor/ beside main.mjs, or
FILIUS_EDITOR_DIR): GET and HEAD only, one wall against leaving the folder,
F's own routes first, assets/ cached a year, the rest asked for again; the
build lays .br and .gz beside the files and F sends the better one the
browser takes (bundle 695 KB to 212 KB).

deploy/Dockerfile: two stages, Node 24, no node_modules, not root.
deploy/docker-compose.yml with an env file per environment: the file sets
the stack's name, volume, image tag and port (test 8081, production 8080).
Measured with both stacks side by side behind nginx and Chromium.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.dockerignore

@@ -0,0 +1,12 @@
+# What the image's build (deploy/Dockerfile) does not need: installed and
+# built things are made anew inside, the oracles and test output stay here,
+# and the environment files hold secrets.
+**/node_modules
+**/dist
+**/*.tsbuildinfo
+.git
+tools
+test-results
+playwright-report
+coverage
+deploy/*.env