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/src/lib/components/layout/SelectionBar.svelte

@@ -22,8 +22,20 @@
 		<button class="count" onclick={() => selectionStore.exit()} title="Clear selection">
 			<span class="num">{$selectionCount}</span>
 			<span class="label">selected</span>
-			<svg class="close-icon" width="14" height="14" viewBox="0 0 14 14" fill="none" aria-hidden="true">
-				<path d="M2 2l10 10M12 2L2 12" stroke="currentColor" stroke-width="1.8" stroke-linecap="round"/>
+			<svg
+				class="close-icon"
+				width="14"
+				height="14"
+				viewBox="0 0 14 14"
+				fill="none"
+				aria-hidden="true"
+			>
+				<path
+					d="M2 2l10 10M12 2L2 12"
+					stroke="currentColor"
+					stroke-width="1.8"
+					stroke-linecap="round"
+				/>
 			</svg>
 		</button>
 
@@ -51,8 +63,14 @@
 	}
 
 	@keyframes slide-up {
-		from { transform: translateY(12px); opacity: 0; }
-		to   { transform: translateY(0);    opacity: 1; }
+		from {
+			transform: translateY(12px);
+			opacity: 0;
+		}
+		to {
+			transform: translateY(0);
+			opacity: 1;
+		}
 	}
 
 	.row {
@@ -135,4 +153,4 @@
 	.delete:hover {
 		background-color: color-mix(in srgb, var(--color-danger) 15%, transparent);
 	}
-</style>
+</style>