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.
