feat(frontend): post collected samples to /api/v1/reports (closes #53)

A Reporter beside AppState POSTs a JSON delta report to the same-origin
/api/v1/reports every reportInterval (default 60s). buildReport is an
exported pure function of host state, emitting each host's unreported,
non-paused samples plus a per-browser clientId, geo null, and a UTC
timestamp; a per-host high-water mark advances only on a delivered POST,
so a failed send re-sends next interval within the history window.
Failure is quiet and never blocks probing.

The client id feature-detects crypto.randomUUID and otherwise builds a v4
id from crypto.getRandomValues, so insecure-context loads (plain HTTP to a
non-localhost host) work; reporter setup is isolated so it can never stop
probing. init() runs only when the #app page is present, so a test can
import buildReport.

vite.config.js proxies /api to 127.0.0.1:8080 for yarn dev.

Model: opus-4-8

vite.config.js

@@ -7,6 +7,13 @@ const commitFull = execSync("git rev-parse HEAD").toString().trim();
 
 export default defineConfig({
     plugins: [tailwindcss()],
+    server: {
+        // Proxy /api to a locally running netwatch-server so `yarn dev`
+        // exercises the real report-posting path.
+        proxy: {
+            "/api": "http://127.0.0.1:8080",
+        },
+    },
     define: {
         __COMMIT_HASH__: JSON.stringify(commitHash),
         __COMMIT_FULL__: JSON.stringify(commitFull),