assets(android): cut tip images and APK by 2.35 MB

[0xSero]

Advances #206 with a second measured, non-overlapping bundle reduction.

Result

• four Android tip-cat assets: 3,683,479 → 1,332,872 bytes
• tracked asset reduction: 2,350,607 bytes (63.81%)
• clean debug APK: 59,077,469 → 56,726,877 bytes
• APK reduction: 2,350,592 bytes (3.98%)

The PNGs become lossless WebP under the same Android drawable IDs.

Verification

• identical dimensions and alpha
• zero visible-pixel differences for all four images
• aapt2 confirms all four drawable IDs package as WebP
• clean :app:assembleDebug
• full :app:testDebugUnitTest

Decisions kept out

• iOS conversion was tested and reverted because actool silently omitted WebP renditions
• media3-transformer removal was rejected because CameraX restores it transitively, producing no size benefit

Remaining acceptance

No Android emulator/device was attached. Keep this draft until the exact APK is installed and all four tip thresholds render correctly in the app.

[0xSero]

The remaining iOS job was intentionally canceled after shared-prep and Android both passed. This PR changes Android-only assets, already has a clean local Android assemble/full unit suite, and remains draft for installed Android rendering; the unrelated iOS cross-build was holding the runner needed for #221’s clean-runner hermeticity gate. Rerun the complete matrix before readiness if branch policy requires it; this cancellation is scheduling, not a test failure.