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

A Reporter class beside AppState POSTs a JSON report to the same-origin
/api/v1/reports every reportInterval (default 60s, a new CONFIG value).
buildReport is a pure function of host state: it emits each host's
unreported, non-paused samples ({t, latency, error}) plus a random
per-browser clientId from localStorage, geo null, and an ISO 8601 UTC
timestamp. A per-host high-water mark keyed on sample time makes every
report a delta and only advances on a delivered POST, so a failed send
re-sends next interval, bounded by the existing history window. Failure
is quiet: one debug-log line per outage, one on recovery, no alert, no
tight retry loop, never blocking probing. While paused nothing is sent.

vite.config.js proxies /api to 127.0.0.1:8080 so yarn dev exercises the
real path against a local netwatch-server. Backend and schema unchanged.

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),