Fix SQLite "database is locked" errors during concurrent task execution

[Copilot]

Multiple scheduled jobs (price updates, currency updates, outage updates, consumption/production updates) accessing the database simultaneously cause SQLite locking errors.

Changes

• Enable WAL mode (PRAGMA journal_mode = WAL) - allows concurrent readers/writers without blocking
• Set busy timeout (PRAGMA busy_timeout = 30000) - wait 30s for locks instead of failing immediately

Applied to both database entry points:

• backend/db/minimal.ts (scheduled jobs)
• backend/db/index.ts (main app)

const database = new Database(fileName, options);

database.exec("PRAGMA journal_mode = WAL");
database.exec("PRAGMA busy_timeout = 30000");

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• cdn.jsdelivr.net
  • Triggering command: /usr/local/bin/deno /usr/local/bin/deno check main.ts (dns block)
  • Triggering command: /usr/local/bin/deno deno test tests/ (dns block)
• dl.deno.land
  • Triggering command: /usr/bin/curl curl -s REDACTED (dns block)
• esm.sh
  • Triggering command: /usr/local/bin/deno /usr/local/bin/deno check main.ts (dns block)
• jsr.io
  • Triggering command: /usr/local/bin/deno /usr/local/bin/deno check main.ts (dns block)
  • Triggering command: /usr/local/bin/deno deno test tests/ (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

Tasks often gives "database is locked" error, especially if many rasks is running at the same time. Investigate.

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