Hide granted permissions, keep screen on for updates, add processing hint

[neteinstein]

Description

Three related Settings/Share UX improvements, all touching feature:settings, feature:share, and core:designsystem:

• Settings permissions section: only lists permissions that aren't granted yet, and the whole "Permissions" section disappears once none remain (currently just POST_NOTIFICATIONS, so today this means the section only shows up if that one permission is missing).
• "Update to latest" reliability: keeps the screen on for the duration of the check/download (KeepScreenOnWhile in SettingsScreen) so a screen timeout mid-download can't drop the install-prompt Intent - Android 10+ silently blocks/drops (doesn't queue) startActivity calls made from a non-foreground app context. SettingsViewModel.downloadAndInstall was also reordered so installPackage(...) fires before updateStatus flips away from Downloading, keeping the screen-on flag active at the exact moment the install intent launches. Also adds explanatory copy above the button that it checks/downloads from the InstaMaps GitHub releases page.
• Share processing screen hint: adds an info banner reassuring the user they can leave/background the app while a share is processing. ProcessSharedUrlWorker already runs as expedited, foreground-notification-backed WorkManager work and posts a result notification when done, so the claim was already true - this just surfaces it in the UI.

WarningBanner (core:designsystem) gains optional actionLabel/onActionClick (default null) to support a purely informational banner with no action, which the new processing-screen hint needed. Backward compatible - the two existing call sites (feature:settings's sideloading warning, feature:share's Instagram-connect nudge) already use named arguments exclusively.

agents.md updated to reflect all three behavior changes.

How to Test

• ./gradlew ktlintCheck compileDebugKotlin compileDebugUnitTestKotlin test (full project) - all pass.
• Manual:
  • Open Settings with POST_NOTIFICATIONS granted - confirm the "Permissions" section is gone entirely.
  • Revoke the notification permission from system Settings, reopen the app's Settings screen - confirm the section reappears listing only that permission.
  • Tap "Update to latest" with a newer release available - confirm the screen stays on (doesn't sleep) through the download, and read the new explanatory text above the button.
  • Share an Instagram/TikTok link into the app - confirm the processing screen shows the new "you can leave, we'll notify you" banner, then background the app and confirm a result notification still arrives.

Checklist

• ./gradlew ktlintCheck passes (or ktlintFormat was run to fix style)
• ./gradlew test passes for all affected modules
• New/changed logic has unit test coverage (domain and data layers especially) - N/A, all changes are in presentation/Compose UI layers, which this project's Kover config excludes from the coverage target (no framework-glue-only test scaffolding exists for these modules).
• agents.md / README.md updated if this changes architecture, setup, or dev workflow
• No secrets, API keys, or credentials committed