Add builder service: scaffold, ASC API, devices UI, fastlane profile manager

Phase 1-3 of the builder subsystem on the Mac mini:
- Express + SQLite + sessions scaffolding, LAN-only service on port 3090
- App Store Connect JWT client (ES256 signing, devices/profiles/bundleIds)
- Device management UI with Apple-side registration
- Fastlane sigh wrapper with profile cache + auto-install to ~/Library/
- launchd plist + deploy script for Mac mini supervision

builder/views/_partial_nav.html

@@ -0,0 +1,10 @@
+<!-- Include pattern note: this file is not served directly; each page hand-inlines the nav for simplicity. -->
+<header>
+  <div class="header-left"><h1>🔨 Builder</h1></div>
+  <nav>
+    <a href="/">Builds</a>
+    <a href="/devices">Devices</a>
+    <a href="/settings">Settings</a>
+    <a href="/logout" class="logout">Logout</a>
+  </nav>
+</header>