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/agents/ResponseProcessor.ts

@@ -223,6 +223,7 @@ async function syncAndBroadcastObservations(
       id: obsId,
       memory_session_id: session.memorySessionId,
       session_id: session.contentSessionId,
+      platform_source: session.platformSource,
       type: obs.type,
       title: obs.title,
       subtitle: obs.subtitle,
@@ -312,6 +313,7 @@ async function syncAndBroadcastSummary(
   broadcastSummary(worker, {
     id: result.summaryId,
     session_id: session.contentSessionId,
+    platform_source: session.platformSource,
     request: summary!.request,
     investigated: summary!.investigated,
     learned: summary!.learned,