add posthog analytics for llm usage and auth events

Captures per-LLM-call token usage tagged by feature (copilot chat,
track block, meeting note, knowledge sync), plus sign-in / sign-out
and identity. Renderer and main share one PostHog identity so events
from either process resolve to the same user.

See apps/x/ANALYTICS.md for the event catalog, person properties,
use-case taxonomy, and how to add new events.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/x/packages/shared/src/ipc.ts

@@ -25,6 +25,13 @@ const ipcSchemas = {
       electron: z.string(),
     }),
   },
+  'analytics:bootstrap': {
+    req: z.null(),
+    res: z.object({
+      installationId: z.string(),
+      apiUrl: z.string(),
+    }),
+  },
   'workspace:getRoot': {
     req: z.null(),
     res: z.object({