Minor fixes: survey media access, Android intent fallback, LOI property refactor

[rfontanarosa]

• Drop per-user scoping of survey media in Storage rules — any user with data-collection permission on a survey can read/write its media, not only the uploading user.
• Add an explicit Play Store fallback URL (S.browser_fallback_url) to the Android intent so the store opens when the app isn't installed (+ tests).
• Extract regenerateLoiProperties (and export propertiesPbToObject) from onCreateLoiHandler for reuse/testability.
• Add a fetchSubmission helper to Datastore.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.13%. Comparing base (019f855) to head (d65c599).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...ding-page/android-intent-landing-page.component.ts	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2569      +/-   ##
==========================================
- Coverage   62.70%   62.13%   -0.58%     
==========================================
  Files         119      121       +2     
  Lines        2896     2947      +51     
  Branches      434      441       +7     
==========================================
+ Hits         1816     1831      +15     
- Misses       1018     1053      +35     
- Partials       62       63       +1     

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[gino-m]

There are a few related things in this one PR. Can you please have an agent split them into multiple PRS?

[rfontanarosa]

closed because it has been split there:
#2575
#2576
#2577