Add local friend profile photo override in nickname editor

[aidanwolter3]

Motivation

• Provide a local-only profile photo override for recipients so a user can set/change a friend’s profile picture for their own view (no network/profile sharing).

Description

• Add a localAvatarUri field to RecipientExtras in app/src/main/protowire/Database.proto to persist a per-recipient local avatar URI.
• Add RecipientTable.setLocalAvatarUri(...) in app/src/main/java/org/thoughtcrime/securesms/database/RecipientTable.kt to update the extras blob with the local URI.
• Expose localAvatarUri() in Recipient.Extras and include it in equality/hash logic, and prefer the local avatar when resolving Recipient.contactPhoto and hasAvatar in app/src/main/java/org/thoughtcrime/securesms/recipients/Recipient.kt so the UI renders the override when present.
• Extend the nickname editor UI in app/src/main/java/org/thoughtcrime/securesms/nicknames/NicknameActivity.kt to add a document picker flow (using ActivityResultContracts.OpenDocument) that persists read permission and triggers NicknameViewModel.onLocalAvatarChanged(...) on selection or removal, and add onAvatarClick/onRemoveAvatarClick callbacks and visible buttons under the avatar preview.
• Add NicknameViewModel.onLocalAvatarChanged(...) in app/src/main/java/org/thoughtcrime/securesms/nicknames/NicknameViewModel.kt to persist the local URI via SignalDatabase.recipients.setLocalAvatarUri(...) on a background dispatcher.
• Add UI strings NicknameActivity__change_photo and NicknameActivity__remove_photo in app/src/main/res/values/strings.xml.

Testing

• Attempted to compile Kotlin with ./gradlew :app:compileDebugKotlin -x lint -x test, but the build could not run in this environment because JAVA_HOME/java is not available, so no automated build/test run completed.

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Codex Task