feat: discover people tab, privacy settings, and friend request button fix

- Add "Discover People" section to Add Friend tab with user cards, mutual counts, and inline actions
- Add discoverStore for fetching/searching discoverable users across local and federated instances
- Add PrivacyPanel to user settings with discoverability toggle
- Add is_discoverable column to users table with migration
- Fix "Send Friend Request" button vertical alignment using transform centering

packages/server/src/utils/sanitize.ts

@@ -17,6 +17,7 @@ export function sanitizeUser(row: typeof schema.users.$inferSelect): User {
       customStatus: null,
       isAdmin: false,
       isDeleted: true,
+      discoverable: false,
       profileUpdatedAt: 0,
       createdAt: row.createdAt,
       homeInstance: null,
@@ -46,6 +47,7 @@ export function sanitizeUser(row: typeof schema.users.$inferSelect): User {
     status: (row.status ?? 'offline') as User['status'],
     customStatus: row.customStatus,
     isAdmin: row.isAdmin === 1,
+    discoverable: row.discoverable !== 0,
     profileUpdatedAt: row.profileUpdatedAt ?? row.createdAt,
     createdAt: row.createdAt,
     homeInstance: row.homeInstance ?? null,