feat: add native SFTP monitors and restore F-Droid - #53

Summary

• split the phone and Wear modules into explicit GitHub and F-Droid distributions so the F-Droid build contains no Play Services Wearable dependency
• publish a dedicated reproducible F-Droid APK with its own SBOM, checksums, and provenance
• add native Uptime Kuma 2.5.4+ SFTP monitor creation and editing with password/private-key authentication and secure saved-secret handling
• preserve paused monitor state during edits
• prepare version 1.3.3 and update the mirrored F-Droid recipe

Verification

• 180 app unit tests passed for both fdroidDebug and githubDebug
• Android lint passed for both phone flavors
• phone GitHub/F-Droid and Wear GitHub release APKs assembled locally
• F-Droid source scanner reported 0 fatal findings with gradle: [fdroid]
• Android QA against Uptime Kuma 2.5.5 covered SFTP creation, private-key/password layouts, saved-secret preservation, and paused-state retention
• Uptime Kuma QA container remained healthy; its only monitor warning was the expected refused connection to the synthetic SFTP target