feat: Windows download link + self-served update feed + install tracking

Downloads/updates:
- config: DOWNLOADS_DIR (override to a mounted volume in prod).
- static.js: serves /downloads/* (installer, latest.yml, .blockmap) with range support for
  resumable + differential auto-updates; /download/windows redirects to the current .exe
  (stable link). Landing page gets a "Download the Windows desktop app" button (hidden in-app).

Install tracking (who installed the app):
- db app_installs + repos.appInstalls (upsert by install_id, fills in the user on sign-in).
- POST /api/v1/telemetry/install (records install + user once authenticated);
  GET /api/v1/admin/installs (admin: list installs with user/version/os/last-seen).
- desktop main.js: stable per-install id in userData, exposed via preload
  (bizConnectNative.installId/version/os); home.html reportInstall() posts it after login.
- e2e: +2 checks (telemetry recorded, admin sees it). 119/119. build batch20.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/config.js

@@ -6,9 +6,13 @@ const PUBLIC_DIR = path.join(__dirname, 'public');
 const REC_DIR = path.join(__dirname, 'recordings');
 const TRANS_DIR = path.join(__dirname, 'transcripts');
 const UPLOADS_DIR = path.join(__dirname, 'uploads');
+// Desktop installers + auto-update feed (latest.yml). Override with DOWNLOADS_DIR to point at a
+// mounted volume in production; IT drops the electron-builder dist/ output here.
+const DOWNLOADS_DIR = process.env.DOWNLOADS_DIR || path.join(__dirname, 'downloads');
 try { fs.mkdirSync(REC_DIR, { recursive: true }); } catch (e) {}
 try { fs.mkdirSync(TRANS_DIR, { recursive: true }); } catch (e) {}
 try { fs.mkdirSync(UPLOADS_DIR, { recursive: true }); } catch (e) {}
+try { fs.mkdirSync(DOWNLOADS_DIR, { recursive: true }); } catch (e) {}
 
 module.exports = {
   PORT: process.env.PORT || 8090,
@@ -17,6 +21,7 @@ module.exports = {
   REC_DIR,
   TRANS_DIR,
   UPLOADS_DIR,
+  DOWNLOADS_DIR,
   SESSION_TTL: 1000 * 60 * 60 * 24, // 24h access-token / cookie lifetime
   REFRESH_TTL: 1000 * 60 * 60 * 24 * 90, // 90d refresh-token lifetime (native clients)
 };