fix(call): end push to talk on ACTION_CANCEL

[tareko]

fix(call): end push to talk on ACTION_CANCEL

Description

The microphone button's touch listener only released push to talk on ACTION_UP. When the long-press ended with MotionEvent.ACTION_CANCEL instead — finger dragged into the system back-gesture edge or navigation bar, notification shade pulled while holding, or any other touch interception — the release branch never ran:

• isPushToTalkActive stayed true
• the WebRTC audio track stayed enabled
• the device kept transmitting room audio indefinitely while the button showed "muted"

A hot-mic privacy bug, and a source of "they hear me although I'm muted" reports.

The release logic is extracted into stopPushToTalk() and now runs for both ACTION_UP and ACTION_CANCEL, pinned by unit tests.

Steps to reproduce / How to test

1. Join a call, microphone muted
2. Long-press the mic button (push to talk activates)
3. End the gesture so it produces ACTION_CANCEL — e.g. drag the finger into the back-gesture edge or pull down the notification shade while holding
4. Ask a remote participant whether they can still hear you

Without this PR: remote keeps hearing you; the button shows "muted".
With this PR: the mic is muted as soon as the gesture ends, regardless of how it ends.

Also verify regular PTT behavior is unchanged: long-press to talk, release to mute; tap toggles mute as before.

• ⛑️ Tests are included (CallActivityPushToTalkTest)
• 🔖 Capability is checked or not needed
• 🔙 Backport requests or not needed
• 📅 Milestone is set
• 🌸 PR title is meaningful

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Note: This PR was developed with AI assistance (opencode / Kimi-K3).

[github-actions]

APK file: https://github.com/nextcloud/talk-android/actions/runs/32628493666/artifacts/9490447059
To test this change/fix you can simply download above APK file and install and test it in parallel to your existing Nextcloud app.
(please click on link to get QR code displayed)

[Copilot]

Pull request overview

Fixes a privacy-critical push-to-talk edge case in CallActivity where touch sequences ending in MotionEvent.ACTION_CANCEL could leave the microphone transmitting indefinitely while the UI appeared muted.

Changes:

• Treat ACTION_CANCEL the same as ACTION_UP for push-to-talk release detection.
• Extract push-to-talk release logic into stopPushToTalk() for reuse and clarity.
• Add unit tests covering push-to-talk release detection (ACTION_UP, ACTION_CANCEL, and non-release actions).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
app/src/main/java/com/nextcloud/talk/activities/CallActivity.kt	Adds a shared stop helper and ends PTT on both ACTION_UP and ACTION_CANCEL.
app/src/test/java/com/nextcloud/talk/activities/CallActivityPushToTalkTest.kt	Adds unit tests to pin expected release-action behavior.

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