Enhancement: Implement support for Classified Conversations (Fixes #6414)

[thirumani-vihaan]

Resolves #6414

This PR implements client-side support for "Classified Conversations", matching the behavior implemented in the Nextcloud backend and web frontend. Classified conversations are highly restricted rooms where data-leaking features are strictly prohibited.

📝 Key Changes:

• Detection & Core Logic: Added SpreedFeatures.CLASSIFIED_CONVERSATIONS capability check and bitwise masking (TalkRoom.attributes & 4) through a unified ConversationUtils.isClassified(...) method.
• Message Restrictions: Hidden "Forward", "Forward to note to self", "Reply privately", and "Translate" actions in the MessageActionsBottomSheet.
• Media Protection: Forced image loadedImage to null for classified messages in Jetpack Compose to naturally trigger the server-provided Blurhash fallback, preventing full image downloads.
• Conversation Settings Restricted: Locked "Sensitive conversation" to true. Hidden SIP dial-in/out, guests allowed, webinar settings, share link, and recording consent toggles.
• Call Recording Disabled: Bypassed the moderator check in CallActivity to completely disable the call recording button in classified rooms.
• Retention & Data Modeling: Added CLASSIFIED to ConversationEnums.ObjectType and hooked up retentionOfClassifiedRoom to properly display the auto-deletion warning banner.
• UI Banner: Added a blinking, Material Theme compliant 🛡️ Classified conversation banner to the ChatToolbar.

🖼️ Screenshots

🏚️ Before	🏡 After
(Upload a screenshot of a standard conversation here)	(Upload a screenshot showing the blinking 🛡️ Classified conversation banner and disabled settings here)

🚧 TODO

• Plumb isClassified through UI state
• Restrict message actions
• Implement Blurhash rendering
• Restrict Call Recording and Conversation Settings

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not needed
• 🔖 Capability is checked or not needed
• 🔙 Backport requests are created or not needed: /backport to stable-xx.x
• 📅 Milestone is set
• 🌸 PR title is meaningful (if it should be in the changelog: is it meaningful to users?)

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI

[mahibi]

Hi @thirumani-vihaan thank you for contributing 👍 . We will review soon