style(project): format Go with gofmt, set up Prettier for the frontend

Run gofmt -w across the backend, normalising the manually-aligned := blocks
to the gofmt standard. No code behaviour changes.

Add Prettier (+ prettier-plugin-svelte) to the frontend with the SvelteKit
default config (tabs, single quotes) so formatting is reproducible, then run
it over the whole tree. Add format / format:check npm scripts and a
.prettierignore (build output, generated schema.ts, static assets).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/.prettierignore

@@ -0,0 +1,11 @@
+# Build output and dependencies
+.svelte-kit
+build
+node_modules
+package-lock.json
+
+# Generated from openapi.yaml — formatting would be overwritten on regen
+src/lib/api/schema.ts
+
+# Static assets (fonts, icons, manifest, robots)
+static