chore: migrate Android app to Capacitor 8

[Inmerson]

Summary

• Migrates the Android app from Capacitor 6 to Capacitor 8.
• Uses @capacitor/android / @capacitor/core 8.5.2.
• Pins @capacitor/cli to exact 8.4.3 because the current 8.5.x CLI line carries an xcode -> uuid advisory that is irrelevant to this Android-only project but still affects npm audit.
• Updates Android build configuration to the Capacitor 8 requirements: AGP 8.13.0, SDK 36, Java 21, current AndroidX/Cordova versions. Existing Gradle wrapper 8.14.3 was already correct.

Verification

Fresh verification on this exact commit:

• Node 22 TypeScript typecheck: passed.
• Vitest: 5/5 files, 12/12 tests passed.
• Vite production build: passed.
• cap sync android: passed with CLI 8.4.3.
• Android assembleDebug --no-daemon: BUILD SUCCESSFUL, 93 tasks.
• npm audit --json: 0 vulnerabilities.
• npm ci --dry-run --ignore-scripts: passed.
• git diff --check: passed.
• Independent review: APPROVED, no Critical/Important/Minor findings.
• GitHub CI: passed.

Dependency context

Dependency refresh PR #23 is merged into main. This PR is now based directly on main and contains only the Capacitor/Android migration on top of that merged refresh.

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