Fix: migrate forecast_points.wind_dir_deg on existing deployments

CREATE TABLE IF NOT EXISTS is a no-op against a table that already exists —
it doesn't add columns introduced after the first deploy. The live LXC's
forecast_points was created before wind_dir_deg existed, so every insert
in lib/weather-fetch.js has been failing with 'column wind_dir_deg of
relation forecast_points does not exist' since that feature landed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/src/db.js

@@ -60,6 +60,13 @@ export async function initDb() {
       updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
     );
   `)
+
+  // wind_dir_deg was added to forecast_points after the first deploy already ran —
+  // CREATE TABLE IF NOT EXISTS above is a no-op against an existing table, it does
+  // NOT retroactively add new columns, so this needs its own explicit migration.
+  // forecast_astro/config didn't need this since they're whole new tables, which
+  // CREATE TABLE IF NOT EXISTS does handle correctly on an existing database.
+  await pool.query(`ALTER TABLE forecast_points ADD COLUMN IF NOT EXISTS wind_dir_deg NUMERIC`)
 }
 
 export async function getStatus() {