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/types/database.ts

@@ -103,6 +103,7 @@ export interface UserPromptRecord {
   prompt_number: number;
   prompt_text: string;
   project?: string;  // From JOIN with sdk_sessions
+  platform_source?: string;
   created_at: string;
   created_at_epoch: number;
 }
@@ -115,6 +116,7 @@ export interface LatestPromptResult {
   content_session_id: string;
   memory_session_id: string;
   project: string;
+  platform_source: string;
   prompt_number: number;
   prompt_text: string;
   created_at_epoch: number;