fix(web): expose GitHub install handlers, simplify Alpine loader, explicit Flask threading (#305)

A user reported that buttons in the v3 web UI were unresponsive in Safari
after a fresh install. The screenshots showed Alpine.js actually running
fine end-to-end — the real issues are a narrow handler-exposure bug and
some latent brittleness worth cleaning up at the same time.

plugins_manager.js: attachInstallButtonHandler and setupGitHubInstallHandlers
were declared inside the main IIFE, but the typeof guards that tried to
expose them on window ran *outside* the IIFE, so typeof always evaluated
to 'undefined' and the assignments were silently skipped. The GitHub
"Install from URL" button therefore had no click handler and the console
printed [FALLBACK] attachInstallButtonHandler not available on window on
every load. Fixed by assigning window.attachInstallButtonHandler and
window.setupGitHubInstallHandlers *inside* the IIFE just before it closes,
and removing the dead outside-the-IIFE guards.

base.html: the Alpine.js loader was a 50-line dynamic-script + deferLoadingAlpine
+ isAPMode branching block. script.defer = true on a dynamically-inserted
<script> is a no-op (dynamic scripts are always async), the
deferLoadingAlpine wrapper was cargo-culted, and the AP-mode branching
reached out to unpkg unnecessarily on LAN installs even though
alpinejs.min.js already ships in web_interface/static/v3/js/. Replaced
with a single <script defer src="..."> tag pointing at the local file plus
a small window-load rescue that only pulls the CDN copy if window.Alpine
is still undefined.

start.py / app.py: app.run() has defaulted to threaded=True since Flask
1.0 so this is not a behavior change, but the two long-lived
/api/v3/stream/* SSE endpoints would starve every other request under a
single-threaded server. Setting threaded=True explicitly makes the
intent self-documenting and guards against future regressions.

Co-authored-by: Chuck <chuck@example.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web_interface/app.py

@@ -726,4 +726,6 @@ def check_health_monitor():
             _threading.Thread(target=_run_startup_reconciliation, daemon=True).start()
 
 if __name__ == '__main__':
-    app.run(host='0.0.0.0', port=5000, debug=True)
+    # threaded=True is Flask's default since 1.0 but stated explicitly so that
+    # long-lived /api/v3/stream/* SSE connections don't starve other requests.
+    app.run(host='0.0.0.0', port=5000, debug=True, threaded=True)