feat: isolate Claude and Codex session sources

Persist platform_source across session creation, transcript ingestion, API query paths, and viewer state so Claude and Codex data can coexist without bleeding into each other.

- add platform-source normalization helpers and persist platform_source in sdk_sessions via migration 24 with backfill and indexing
- thread platformSource through CLI hooks, transcript processing, context generation, pagination, search routes, SSE payloads, and session management
- expose source-aware project catalogs, viewer tabs, context preview selectors, and source badges for observations, prompts, and summaries
- start the transcript watcher from the worker for transcript-based clients and preserve platform source during Codex ingestion
- auto-start the worker from the MCP server for MCP-only clients and tighten stdio-driven cleanup during shutdown
- keep createSDKSession backward compatible with existing custom-title callers while allowing explicit platform source forwarding

src/services/worker/SessionManager.ts

@@ -77,6 +77,9 @@ export class SessionManager {
         });
         session.project = dbSession.project;
       }
+      if (dbSession.platform_source && dbSession.platform_source !== session.platformSource) {
+        session.platformSource = dbSession.platform_source;
+      }
 
       // Update userPrompt for continuation prompts
       if (currentUserPrompt) {
@@ -144,6 +147,7 @@ export class SessionManager {
       contentSessionId: dbSession.content_session_id,
       memorySessionId: null,  // Always start fresh - SDK will capture new ID
       project: dbSession.project,
+      platformSource: dbSession.platform_source,
       userPrompt,
       pendingMessages: [],
       abortController: new AbortController(),