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/.prettierrc

@@ -0,0 +1,15 @@
+{
+	"useTabs": true,
+	"singleQuote": true,
+	"trailingComma": "none",
+	"printWidth": 100,
+	"plugins": ["prettier-plugin-svelte"],
+	"overrides": [
+		{
+			"files": "*.svelte",
+			"options": {
+				"parser": "svelte"
+			}
+		}
+	]
+}