feat: add share image to diary entry #340

[wellorbetter]

Description

Add "Share to Daily You" to the Android share sheet. When triggered, a new page opens allowing the user to add the shared image to a diary entry — either today's or a date they pick.

Closes #340

Reasoning

Used an Android intent-filter with ACTION_SEND + image/* MIME type to receive shares. A MethodChannel in MainActivity
passes the content URI to Flutter. ShareIntentService converts the URI to a local file path, and ShareToEntryPage handles UI
for date selection and saving to the entry via the existing EntriesProvider / EntryImagesProvider pattern.

Testing

1. Long-press an image in the gallery → share → select "Daily You" → verify page opens with image preview
2. Select today → tap "Add to Entry" → verify image appears in today's diary entry
3. Select a past date → tap "Add to Entry" → verify image is appended to that date's entry
4. Share to a date with an existing entry → verify image is appended (not replaced)
5. Tap back/cancel → verify no entry is created
6. Test with app not running → verify app launches directly to the share page

Type of change

❌ Bug fix
✅ New feature (A non-breaking change that adds functionality)
❌ Breaking change
❌ Refactor
❌ Performance
❌ Style
❌ Docs
❌ Chore

[wellorbetter]

This PR implements receive-share for images (issue #340) — users can share images from gallery/other apps directly into a diary entry.

How it works:

• Android intent-filter registers the app as a share target for image/*
• MainActivity handles both cold-start (stores URIs until Flutter is ready) and warm-start (pushes URIs via MethodChannel stream)
• ShareIntentService bridges Android → Flutter, reads content:// URIs and compresses images
• ShareToEntryPage lets the user pick today or a custom date, then saves via the existing EntryImagesProvider — no changes to
  existing save logic

What was changed:

• AndroidManifest.xml — added intent-filter (2 actions)
• MainActivity.kt — added MethodChannel + intent handling
• 3 new Flutter files: share_intent_service.dart, share_to_entry_page.dart, share_image_preview.dart
• Minimal changes to home_page.dart, mobile_scaffold.dart, launch_page.dart, main.dart, launch_intent.dart (routing only)
• l10n: all 31 languages translated