Improve release scripts and make workflows manual

Redirect script informational/warning output to stderr and improve robustness of release tooling. Changes include:

- Redirect many echo messages to stderr so scripts can emit machine-readable output on stdout.
- Extract-release-notes: better parsing of CHANGELOG entries (tries v-prefixed and non-prefixed headings, cleaner note formatting) and improved fallbacks when changelog is missing.
- Extract-version: accept versions with +build or -suffix, add diagnostic output when pubspec is missing, and tighten validation.
- Setup/verify APK signing: more consistent stderr logging and clearer warnings; ensure keystore decoding/logging is visible.
- Minor script usage message fixes (generate-tag-name, attach-apk-to-release).
- CI/workflows: change backend-foundation, mobile-ci, and web-quality triggers to workflow_dispatch (manual runs); update product-release (make scripts step label emoji, remove node cache lines, bump Flutter to 3.38.x).

These changes improve CI reliability, make scripts friendlier for automated consumers, and fix release note/version parsing edge cases.

.github/workflows/mobile-ci.yml

@@ -1,16 +1,7 @@
 name: Mobile CI
 
 on:
-  pull_request:
-    paths:
-      - 'apps/mobile/**'
-      - '.github/workflows/mobile-ci.yml'
-  push:
-    branches:
-      - main
-    paths:
-      - 'apps/mobile/**'
-      - '.github/workflows/mobile-ci.yml'
+  workflow_dispatch:
 
 jobs:
   detect-changes: