fix(server): run assets.deploy as a mix release step

Without this, 'mix release' produced a tarball that had app.css/app.js
(so LiveView worked) but was missing cache_manifest.json and the digested
asset paths. Phoenix served the bare files OK, but the client-side
LiveView bootstrap timing was fragile: if a form was submitted before
the LiveSocket attached, the browser fell back to a native HTML GET,
producing bug-report URLs like /admin/hosts?host%5Bname%5D=repl.

Define a project releases/0 with a pre-assemble step that runs
assets.deploy, so minified + digested assets are baked into every
release tarball.

Also gitignore digested priv/static artifacts so dev-time byproducts
don't pollute commits.

.gitignore

@@ -26,6 +26,20 @@
 /agent/burrito_out/
 /agent/dist/
 
+# Phoenix digest artifacts (built into release; shouldn't be committed)
+/server/priv/static/assets/
+/server/priv/static/cache_manifest.json
+/server/priv/static/*-*.ico
+/server/priv/static/*-*.txt
+/server/priv/static/*-*.txt.gz
+/server/priv/static/*.gz
+/server/priv/static/images/*-*
+/server/priv/static/images/*.gz
+
+# Playwright / screenshots (local verification artifacts)
+/.playwright-mcp/
+/*.png
+
 # Editors / OS
 .DS_Store
 .vscode/