Element X can't start a DM when the server refuses encrypted rooms

Element X always requests an encrypted room when you start a DM. If the homeserver refuses encrypted rooms, room creation fails and all the user sees is "An error occurred when trying to start a chat". From the phone there is then no way to start a conversation at all.

We run Synapse with encryption off. That is deliberate: our rooms carry bots and widgets that would go silent, and we would lose server side search on a server we host ourselves. Synapse enforces it through `default_power_level_content_override`, putting `m.room.encryption` above the level anyone reaches, and it rejects the create call before the room exists:

```
SynapseError: 403 - You cannot create an encrypted room. user_level (100) < send_level (999)
POST /_matrix/client/v3/createRoom 403 "Element X/26.07.4 (Mac; ...)"
```

Element Web and Element Desktop hit the same endpoint a minute earlier and got a 200, because they read `io.element.e2ee.force_disable` from the client well-known, which we publish:

```json
"io.element.e2ee": { "default": false, "force_disable": true }
```

### Reproducing it

1. Configure Synapse to refuse encrypted rooms (`encryption_enabled_by_default_for_room_type: off`, plus an `m.room.encryption` power level nobody has).
2. Serve `io.element.e2ee.force_disable: true` in `/.well-known/matrix/client`.
3. Search for a user in Element X and start a chat.

You expect an unencrypted DM, the same one Element Web creates. You get an error dialog.

### Half of this already exists on iOS

https://github.com/element-hq/element-x-ios/pull/5866 replaced the hardcoded `isEncrypted: true` in `ClientProxy` with `!appSettings.forceDisableE2EE.publisher.value`, and that shipped in 26.07.4. But nothing in the open source tree ever sets the flag. `forceDisableE2EE` is a `RemotePreference` defaulting to `false` and no code calls `applyRemoteValue` on it. The PR says it is controlled by Element Pro, which leaves self hosted servers where they started.

Android does not have the flag at all. `RustMatrixClient.createDM` still passes `isEncrypted = true` with nothing to override it.

### What we are asking for

Let the homeserver set that flag, not just Element Pro. `io.element.e2ee.force_disable` already means exactly this and Element Web honours it, so the value is sitting there unread. `RemoteSettingsHook` fetches `.well-known/element/element.json` already and decodes `enforce_element_pro`, and the MapTiler setting shows the pattern of pushing a well-known value into a `RemotePreference`. And the same flag on Android.

As it stands, Element X is unusable as a mobile client on any server that turns encryption off, other than for reading along. Which is a pity, because it is otherwise the nicer of the two mobile apps.

Start with iOS ClientProxy and the RemotePreference forceDisableE2EE flow, including RemoteSettingsHook and applyRemoteValue; compare that with Android's RustMatrixClient.createDM. Verify how the client well-known value is decoded, then confirm that force_disable reaches both clients and allows an unencrypted DM when the homeserver rejects encrypted rooms.

Written by the indexing model from the issue text.