fix(shared): drop .js extensions from relative imports for Metro

packages/shared/src/index.ts and all sub-modules used .js extensions on
relative imports (e.g. './admin/index.js') pointing at .ts source files.
TypeScript with moduleResolution: "Bundler" doesn't need them, and
Metro's eager exporter (used for preview / production builds) reads
them literally and fails — only the dev-server Metro fell back to .ts.

Workspace typecheck remains 8/8 green; Vite and TS Bundler resolution
already accept both styles, so desktop is unaffected.

packages/shared/src/chat/groups.ts

@@ -1,5 +1,5 @@
-import type { AppSupabaseClient } from '../supabase/client.js';
-import type { MemberRole } from '../supabase/types.js';
+import type { AppSupabaseClient } from '../supabase/client';
+import type { MemberRole } from '../supabase/types';
 
 async function currentUserId(client: AppSupabaseClient): Promise<string> {
   const { data, error } = await client.auth.getUser();
@@ -14,7 +14,7 @@ export interface CreateGroupParams {
   memberUserIds: string[];
 }
 
-// Client-side 3-step create: conversation → self as admin → peers as members.
+// Client-side 3-step create: conversation → self as admin → peers as members.
 // On any peer-insert failure the conversation still survives (partial group is
 // still usable, admin can retry). On self-insert failure we delete the empty
 // conversation to avoid orphans.
@@ -24,7 +24,7 @@ export async function createGroup(params: CreateGroupParams): Promise<string> {
   if (trimmed.length === 0) throw new Error('group name required');
 
   // Generate the uuid client-side so we don't need a post-insert SELECT on
-  // conversations — the SELECT policy requires membership, which only exists
+  // conversations — the SELECT policy requires membership, which only exists
   // AFTER we insert the creator's member row in step 2.
   const conversationId = crypto.randomUUID();