Add Wear setting to reserve Vibration Watch gestures

[willbilec]

Two-finger single and double taps are intercepted by sideloaded Backtalk on Samsung watches, preventing Vibration Watch from responding. Add a Wear-only Reserve gestures for Vibration Watch switch in Advanced Settings, off by default, that reports these two gestures as unhandled before gesture feedback, training, menus, recording, or assigned actions.

The switch takes effect immediately and preserves saved gesture assignments. The two assignment rows explain that the gestures are reserved while enabled; switching it off restores their availability. Other gestures and the existing system-app Vibration Watch integration are preserved.

Validation

• All 290 Wear unit tests passed, including three new policy tests covering defaults, Wear versus phone, gesture IDs, and immediate switching.
• Wear debug APK built successfully; phone Java/Kotlin compilation passed.
• Installed on a Samsung Galaxy Watch. The user enabled the switch and confirmed that Vibration Watch works with Backtalk enabled.
• git diff --check passed.

[aaron-gh]

I checked this against master:

• The switch shows on watches, since they use the main advanced_preferences.xml, and it's hidden on phones.
• Gestures from the framework's onGesture and from Backtalk's own gesture detector both go through handleOnGestureById, so returning early there covers both.
• A manual switch is needed: SettingsUtils.isVibrationWatchEnabled only works for system apps, so for sideloaded Backtalk it's always false.

Small things:

• In strings.xml, the new strings went in between the speakerphone title's comment ("Title of the setting that moves calls to the speaker…") and its string. That comment now sits above the Vibration Watch title, and the new strings have no comments for translators.
• differences.md needs an entry for the setting, under "Wear OS watches > Gestures on watches".
• While the switch is on, two-finger tap and two-finger double tap lose their Backtalk actions on the watch. By default those are pause or resume speech, and media control or voice input. The docs entry should say so.