Budget: per-person expense tracking with member chips

- New budget_item_members junction table (migration 27)
- Assign trip members to budget items via avatar chips in Persons column
- Per-person split auto-calculated from assigned member count
- Per-person summary integrated into total budget card
- Member chips rendered via portal dropdown (no overflow clipping)
- Mobile: larger touch-friendly chips (30px) under item name
- Desktop: compact chips (20px) in Persons column
- Custom NOMAD-style tooltips on chips
- WebSocket live sync for all member operations
- Fix invite button text color in dark mode
- Widen budget layout to 1800px max-width
- Shorten "Per Person/Day" column header

server/src/db/database.js

@@ -569,6 +569,20 @@ function initDb() {
         `);
       } catch {}
     },
+    // 27: Budget item members (per-person expense tracking)
+    () => {
+      _db.exec(`
+        CREATE TABLE IF NOT EXISTS budget_item_members (
+          id INTEGER PRIMARY KEY AUTOINCREMENT,
+          budget_item_id INTEGER NOT NULL REFERENCES budget_items(id) ON DELETE CASCADE,
+          user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+          paid INTEGER NOT NULL DEFAULT 0,
+          UNIQUE(budget_item_id, user_id)
+        );
+        CREATE INDEX IF NOT EXISTS idx_budget_item_members_item ON budget_item_members(budget_item_id);
+        CREATE INDEX IF NOT EXISTS idx_budget_item_members_user ON budget_item_members(user_id);
+      `);
+    },
     // Future migrations go here (append only, never reorder)
   ];