Update README changelog, remove Firebug IT branding, retire dead mobile middleware

README.md: backfill the Changelog with the 2026.9.5, 2026.8.31.1, 2026.8.31,
and v1.2.0 releases that were missing (it jumped straight from 1.0.0 to
1.1.0). Also correct the stale "Mobile App Support"/"Mobile App
Integration" sections - the native Android app is retired, and the
sync protocol they describe now powers the offline PWA instead.

Remove Firebug IT branding/contact info across README.md, API.md, and
the site footer, and drop the stale tasks.firebugit.com fallback from
development.py's ALLOWED_HOSTS/CSRF_TRUSTED_ORIGINS.

AllowMobileAppFramingMiddleware detected the native app via a
'com.firebugit.keepitgoing' User-Agent check to allow WebView iframe
embedding. With that app retired, replaced it with
SecurityHeadersMiddleware, which applies the same X-Frame-Options/CSP
headers unconditionally instead of only for non-mobile requests -
same protection for real users, dead branch and dead branding gone.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tasks/middleware/security_headers.py

@@ -0,0 +1,35 @@
+"""
+Middleware that applies clickjacking protection headers to every response.
+
+Previously also allowed iframe embedding for a native mobile app's WebView
+(detected via User-Agent); that app has been retired in favor of the PWA,
+so the headers are now applied unconditionally.
+"""
+
+
+class SecurityHeadersMiddleware:
+    """Add X-Frame-Options and a CSP frame-ancestors policy to every response."""
+
+    def __init__(self, get_response):
+        self.get_response = get_response
+
+    def __call__(self, request):
+        response = self.get_response(request)
+
+        if 'X-Frame-Options' not in response:
+            response['X-Frame-Options'] = 'DENY'
+
+        if 'Content-Security-Policy' not in response:
+            response['Content-Security-Policy'] = (
+                "default-src 'self'; "
+                "script-src 'self' 'unsafe-inline'; "
+                "style-src 'self' 'unsafe-inline'; "
+                "img-src 'self' data: https:; "
+                "font-src 'self' data:; "
+                "connect-src 'self'; "
+                "frame-ancestors 'none'; "
+                "base-uri 'self'; "
+                "form-action 'self';"
+            )
+
+        return response