Static and Dynamic capabilities: provide all configs and preferences as capabilities with 2 hashes for critical and mutable subsets

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Current proposal:

1. Add all the preferencies to the capabilities (e.g., PlaySound is missing)
   • InitialState should be only used for web-only preloaded initial state of the application (for example, to include all the conversations in the initial response). But never for client-required data
   • See also:
     • https://github.com/nextcloud/spreed/issues/8715
     • https://github.com/nextcloud/spreed/issues/14999
2. Indirectly (without the structure change) divide all the capability values into 2 subsets:
   1. With actually critical-to-change values requiring application restart to apply
      • For instance: backend version, federation.enabled, HPB-related configs
   2. With changeable configs
      • The most of the configs and conditional features
3. Add two new hash headers for the values above
   1. Aka X-Nextcloud-Talk-Capabilities-Static-Hash (or, immutable, persistent)
   2. Aka X-Nextcloud-Talk-Capabilities-Dynamic-Hash (or mutable, fluid)
4. The current 'X-Nextcloud-Talk-Hash header includes both types of values is kept for backward compatibility
5. On Frontend:
   1. On top of the existing capability manager, add a reactive store adapter
   2. Provide public API:
      • Get capabilities
      • (Un)Subscribe to hashes invalidation
      • (Un)Subscribe to capability change

No files or tests are named. Start by locating the existing capability manager and handling for the X-Nextcloud-Talk-Hash header, then trace how capabilities are exposed to the frontend; done means the proposed static and dynamic hashes, backward-compatible header, and subscription APIs are defined across the affected layers.