feat(dictation): gate streaming dictation behind a workspace toggle

Streaming (silence-cut) dictation was hardcoded on. Put it behind a per-workspace
flag settings.ai.dictationStreaming, default off, with batch dictation as the
default and fallback. Mirrors the existing settings.ai.dictation flag end to end:

- server: aiDictationStreaming on UpdateWorkspaceDto + workspace.service writes
  settings.ai.dictationStreaming via updateAiSettings (jsonb merge keeps siblings)
- client: IWorkspaceAiSettings.dictationStreaming, an optimistic "Streaming
  dictation" sub-toggle under "Voice dictation" (disabled when dictation is off)
- gate the MicButton streaming prop in the editor toolbar and chat composer on
  the flag instead of a literal true

When the flag is absent/false both call sites pass streaming=false, so the VAD
model/wasm are never fetched and behavior is unchanged. Reuses the existing STT
model and /ai-chat/transcribe — no new provider/model/endpoint fields.

Removes the backlog entry now that it is implemented.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/server/src/core/workspace/dto/update-workspace.dto.ts

@@ -55,6 +55,10 @@ export class UpdateWorkspaceDto extends PartialType(CreateWorkspaceDto) {
   @IsBoolean()
   aiDictation: boolean;
 
+  @IsOptional()
+  @IsBoolean()
+  aiDictationStreaming: boolean;
+
   // Workspace master toggle that enables/disables the HTML embed block type.
   // Persisted at settings.htmlEmbed. ABSENT/false => OFF (default). The block
   // itself renders in a sandboxed iframe, so this is a feature switch, not a

apps/server/src/core/workspace/services/workspace.service.ts

@@ -511,6 +511,20 @@ export class WorkspaceService {
         );
       }
 
+      if (typeof updateWorkspaceDto.aiDictationStreaming !== 'undefined') {
+        const prev = settingsBefore?.ai?.dictationStreaming ?? false;
+        if (prev !== updateWorkspaceDto.aiDictationStreaming) {
+          before.aiDictationStreaming = prev;
+          after.aiDictationStreaming = updateWorkspaceDto.aiDictationStreaming;
+        }
+        await this.workspaceRepo.updateAiSettings(
+          workspaceId,
+          'dictationStreaming',
+          updateWorkspaceDto.aiDictationStreaming,
+          trx,
+        );
+      }
+
       if (typeof updateWorkspaceDto.htmlEmbed !== 'undefined') {
         const prev = settingsBefore?.htmlEmbed ?? false;
         if (prev !== updateWorkspaceDto.htmlEmbed) {
@@ -564,6 +578,7 @@ export class WorkspaceService {
       delete updateWorkspaceDto.allowMemberTemplates;
       delete updateWorkspaceDto.aiChat;
       delete updateWorkspaceDto.aiDictation;
+      delete updateWorkspaceDto.aiDictationStreaming;
       delete updateWorkspaceDto.htmlEmbed;
       delete updateWorkspaceDto.trackerHead;
       delete updateWorkspaceDto.aiPublicShareAssistant;