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/cli/handlers/session-init.ts

@@ -12,6 +12,7 @@ import { HOOK_EXIT_CODES } from '../../shared/hook-constants.js';
 import { isProjectExcluded } from '../../utils/project-filter.js';
 import { SettingsDefaultsManager } from '../../shared/SettingsDefaultsManager.js';
 import { USER_SETTINGS_PATH } from '../../shared/paths.js';
+import { normalizePlatformSource } from '../../shared/platform-source.js';
 
 export const sessionInitHandler: EventHandler = {
   async execute(input: NormalizedHookInput): Promise<HookResult> {
@@ -42,6 +43,7 @@ export const sessionInitHandler: EventHandler = {
     const prompt = (!rawPrompt || !rawPrompt.trim()) ? '[media prompt]' : rawPrompt;
 
     const project = getProjectName(cwd);
+    const platformSource = normalizePlatformSource(input.platform);
 
     logger.debug('HOOK', 'session-init: Calling /api/sessions/init', { contentSessionId: sessionId, project });
 
@@ -52,7 +54,8 @@ export const sessionInitHandler: EventHandler = {
       body: JSON.stringify({
         contentSessionId: sessionId,
         project,
-        prompt
+        prompt,
+        platformSource
       })
     });