docs: publish Android compatibility matrix

[zefutoff]

Publish the first reproducible Android application compatibility matrix.

The matrix records:

• physical device and Android version;
• exact tested application versions;
• tested project revision;
• SpellCheckerService behavior;
• PROCESS_TEXT behavior;
• IME/InputConnection behavior;
• application-specific limitations and fallbacks.

Current physical-device coverage includes:

• Samsung Notes;
• Firefox;
• Samsung Messages;
• Chrome;
• Android System WebView;
• Proton Mail;
• K-9 Mail;
• WhatsApp.

Also included:

• a helper script for reproducibly collecting device and application-version metadata;
• README linkage to the compatibility documentation;
• roadmap completion for messaging/mail, Chromium/WebView and compatibility documentation;
• changelog entry.

Validation:

• shellcheck tools/*.sh
• actionlint
• JavaScript bridge contract
• ktlint
• JVM tests
• Android lint
• make check
• make assemble

The documented results intentionally retain the exact project revision used for each manual test rather than implying that every application was retested on the latest commit.