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/shared/platform-source.ts

@@ -0,0 +1,36 @@
+export const DEFAULT_PLATFORM_SOURCE = 'claude';
+
+function sanitizeRawSource(value: string): string {
+  return value.trim().toLowerCase().replace(/\s+/g, '-');
+}
+
+export function normalizePlatformSource(value?: string | null): string {
+  if (!value) return DEFAULT_PLATFORM_SOURCE;
+
+  const source = sanitizeRawSource(value);
+  if (!source) return DEFAULT_PLATFORM_SOURCE;
+
+  if (source === 'transcript') return 'codex';
+  if (source.includes('codex')) return 'codex';
+  if (source.includes('cursor')) return 'cursor';
+  if (source.includes('claude')) return 'claude';
+
+  return source;
+}
+
+export function sortPlatformSources(sources: string[]): string[] {
+  const priority = ['claude', 'codex', 'cursor'];
+
+  return [...sources].sort((a, b) => {
+    const aPriority = priority.indexOf(a);
+    const bPriority = priority.indexOf(b);
+
+    if (aPriority !== -1 || bPriority !== -1) {
+      if (aPriority === -1) return 1;
+      if (bPriority === -1) return -1;
+      return aPriority - bPriority;
+    }
+
+    return a.localeCompare(b);
+  });
+}