Add paycheck-centric main view

Two-column monthly view showing bills, amounts, paid status,
and remaining balance per paycheck. Month navigation included.
Also adds PATCH /api/paycheck-bills/:id/paid endpoint.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/src/routes/paychecks.js

@@ -232,4 +232,37 @@ router.get('/paychecks/months', async (req, res) => {
   }
 });
 
+// PATCH /api/paycheck-bills/:id/paid
+router.patch('/paycheck-bills/:id/paid', async (req, res) => {
+  const id = parseInt(req.params.id, 10);
+  if (isNaN(id)) {
+    return res.status(400).json({ error: 'Invalid id' });
+  }
+
+  const { paid } = req.body;
+  if (typeof paid !== 'boolean') {
+    return res.status(400).json({ error: 'paid must be a boolean' });
+  }
+
+  try {
+    const result = await pool.query(
+      `UPDATE paycheck_bills
+       SET paid = $1,
+           paid_at = CASE WHEN $1 THEN NOW() ELSE NULL END
+       WHERE id = $2
+       RETURNING id, paid, paid_at`,
+      [paid, id]
+    );
+
+    if (result.rows.length === 0) {
+      return res.status(404).json({ error: 'paycheck_bill not found' });
+    }
+
+    res.json(result.rows[0]);
+  } catch (err) {
+    console.error('PATCH /api/paycheck-bills/:id/paid error:', err);
+    res.status(500).json({ error: 'Failed to update paid status' });
+  }
+});
+
 module.exports = router;