feat(app): share an image into Freegle to start an Offer (Android)

[edwh]

What

Adds an Android "Share → Freegle" target. From the gallery, camera, or any
other app's share sheet, the user can send a photo straight into a new OFFER
with the image already attached — no need to open the app and re-pick it.

This is the Android half of the Share-into-Freegle feature. The iOS Share
Extension follows in a separate PR (it needs an App Group + provisioning-profile
changes, so it's staged on its own to avoid touching production signing here).

How

• AndroidManifest — ACTION_SEND / ACTION_SEND_MULTIPLE image/*
  intent-filters on MainActivity.
• MainActivity.java — on onCreate/onNewIntent, copies the shared
  image(s) from the intent-scoped content:// Uri into the app cache (the Uri
  permission doesn't outlive the intent) and exposes them to the WebView via a
  tiny window.FreegleShare JS bridge (consume() returns the file paths and
  clears the queue).
• stores/mobile.js — initShareIntent pulls shared images at startup (cold
  share) and on resume (warm share), converts the cache paths with
  Capacitor.convertFileSrc, queues them in pendingSharedImages, and routes
  to /give/mobile/photos.
• PhotoUploader.vue — defineExpose({ processPhoto }) so a shared photo
  runs the same quality-check + tus-upload path as the camera/gallery flows.
• give/mobile/photos.vue — on mount, attaches any queued shared image(s),
  then clears the queue.

Risk / testing

• Pure-additive: web behaviour and existing camera/gallery flows are unchanged
  unless the native FreegleShare bridge is present (Android app only).
• Native (manifest + Java) can't be built locally; verified via CI Android build
  and on-device share test.
• No new dependencies.

🤖 Generated with Claude Code

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[edwh]

Companion iOS PR (stacked on this one): #759 — adds the iOS share-sheet extension, dark/flag-gated. Both PRs are in this same repo (Freegle/Iznik); the iOS Share Extension is authored directly under iznik-nuxt3/ios, so no second-repo (e.g. cap7 plugin) change is involved. Merge this Android PR first; #759's base then retargets to master.

[edwh]

Superseded by #766, which consolidates the native-app feature PRs (#756 haptics, #757 app-icon shortcuts, #758 share-into-Freegle Android, #759 share-into-Freegle iOS) into a single PR rebased onto current master. Branch kept (not deleted) in case it's needed.