feat: integrate Supabase OAuth with OIDC discovery for authentication

Add rowboat auth flow using Supabase as the OIDC provider. User info is
fetched via the standard OIDC userinfo endpoint (discovered from issuer
metadata) instead of a hard-coded Supabase URL. Includes login screen,
auth state hook, IPC handlers, logout button, and id_token_sub persistence
for userinfo fetches across app restarts.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

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

@@ -244,6 +244,39 @@ const ipcSchemas = {
       success: z.literal(true),
     }),
   },
+  'auth:getStatus': {
+    req: z.null(),
+    res: z.object({
+      isAuthenticated: z.boolean(),
+      user: z.object({
+        email: z.string(),
+        name: z.string().optional(),
+      }).nullable(),
+    }),
+  },
+  'auth:login': {
+    req: z.null(),
+    res: z.object({
+      success: z.boolean(),
+      error: z.string().optional(),
+    }),
+  },
+  'auth:logout': {
+    req: z.null(),
+    res: z.object({
+      success: z.boolean(),
+    }),
+  },
+  'auth:didAuthenticate': {
+    req: z.object({
+      isAuthenticated: z.boolean(),
+      user: z.object({
+        email: z.string(),
+        name: z.string().optional(),
+      }).nullable(),
+    }),
+    res: z.null(),
+  },
 } as const;
 
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