fix: make server header changes reach installed PWA clients

The service worker precaches index.html together with its response headers, so
a server-only change never reaches an installed client: the client build is
byte-identical, the precache manifest is unchanged, and the worker has no
reason to update. That is why the CSP fix in 1.6.1 did not reach a browser that
already had the app cached — it kept replaying a cached shell carrying the old,
broken CSP, indefinitely.

The release version is now compiled into the client, which makes every release
change the bundle hash, hence index.html, hence its precache revision, hence
sw.js itself — the bytes browsers compare to decide whether to update. Verified
by bumping only the version: index-DYufL2Fa.js -> index-60N_3d5j.js, with the
new name carried into the sw.js manifest.

It also surfaces in the footer, so the deployed version is visible without
digging through devtools.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011uBWhwV3wFQ5MBCcMHHem7

vite.config.ts

@@ -3,9 +3,24 @@ import react from '@vitejs/plugin-react';
 import path from 'path';
 import {defineConfig} from 'vite';
 import { VitePWA } from 'vite-plugin-pwa';
+import { createRequire } from 'module';
+
+const { version } = createRequire(import.meta.url)('./package.json');
 
 export default defineConfig(() => {
   return {
+    /**
+     * The release version, compiled into the client.
+     *
+     * This is load-bearing, not cosmetic. The service worker precaches
+     * index.html *including its response headers*, so a server-side header
+     * change (a CSP fix, say) never reaches an installed PWA: nothing in the
+     * client build changed, the precache manifest is byte-identical, and the
+     * worker has no reason to update. Baking the version in means every release
+     * changes the bundle hash, which changes index.html, which invalidates the
+     * precache and re-fetches the shell with current headers.
+     */
+    define: { __APP_VERSION__: JSON.stringify(version) },
     plugins: [
       react(), 
       tailwindcss(),