Fix Firebase security rules to prevent unauthorized modification/deletion

[Copilot]

The documented Firebase Storage rules allowed full unauthenticated read/write access, enabling anyone to delete or modify arbitrary data. Firestore rules also didn't distinguish create from update/delete, making the security posture inconsistent.

Changes

• Firestore rules: Replace allow read: if true; allow write: if request.auth != null with:

  allow create: if true;
  allow read, update, delete: if request.auth != null;
  

• Storage rules: Replace allow read, write: if true with the same pattern — unauthenticated creates allowed, all other operations require auth.
• Updated descriptive text to accurately reflect the new posture.
• Applied consistently across all versioned docs (v1.0.6, v2.0.2, v2.1.1, v2.2.0) and current docs.

Security posture

Operation	Unauthenticated	Authenticated
Create	✅	✅
Read	❌	✅
Update	❌	✅
Delete	❌	✅

Participants use anonymous Firebase auth and are therefore "authenticated" — this change does not break participant data submission.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Review Firebase security</issue_title>
<issue_description>Our firebase security relies on policy based access. We need to make sure the policies allow the following:

1. Any user can create Firestore and firebase storage items
2. Any user should be able to read and modify the items they created
3. Any authenticated user should have full CRUD access to any document in the repository

We're trying to avoid a problem where unauthorized users can delete/modify documents that are not their own.

Update the Firebase policies to match that posture.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Review Firebase security study#1052

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