feat(android): add photos and camera media strip to block inserter

[jkmassel]

Summary

Adds the recent-photos / Photos / Camera strip between the inserter header and category tabs. Stacked on top of #469; rebase onto trunk once that lands. Independent of #478 (search/filter PR) — they touch different parts of SheetContent.

Three runtime states:

1. Permission rationale card — shown when the host app hasn't been granted READ_MEDIA_IMAGES. The card swaps body copy and primary button label depending on whether we've never asked, were denied once, or were permanently denied. SharedPreferences tracks the first prompt because shouldShowRequestPermissionRationale alone can't distinguish "never asked" from "permanently denied".
2. Recent photos strip — once granted, queries MediaStore for the 12 most recent images, renders as a 2-row thumbnail grid.
3. Photos / Camera tiles — Photos launches the system photo picker (permissionless via PickVisualMedia); Camera launches ACTION_IMAGE_CAPTURE against a cache-scoped FileProvider URI. Hand-off of the picked URI to editor insertion is a follow-up.

The library declares its own FileProvider keyed off \${applicationId} so it won't collide with one a host app already provides. Hosts that don't need photo access can tools:node=\"remove\" the manifest permissions.

Test plan

• First launch: rationale card shows with "Allow" + "Reject"
• Tap Allow → system prompt appears → grant → strip shows recent photos
• Reject system prompt → rationale switches to "Try Again" copy
• Reject system prompt twice (or 'don't ask again') → rationale switches to "Open Settings"
• Tap Reject in rationale → entire strip hides until permission granted via Settings
• Tap Photos tile → system photo picker opens
• Tap Camera tile → camera app opens with cache-scoped output URI
• Vertical drag on the photo strip area still drags the bottom sheet (nested scroll relay)