fix(api): honor self-hosted email sender settings

[izadoesdev]

Alarm notifications ignored configured sender addresses and used the hosted databuddy.cc sender. Resolve them through the existing ALERTS_EMAIL_FROM → EMAIL_FROM fallback, make the example alert override optional, and forward both sender variables through Turbo. Hosted sender defaults and per-alarm overrides remain unchanged.

This six-file change covers notification sender resolution and its delivery regression test, the existing @databuddy/env workspace dependency, .env.example, and Turbo configuration. Self-hosted Compose wiring and setup documentation belong to companion #804; the two PRs can land independently.

Validation: root bun run lint, all 33 typecheck tasks, and all 27 root test tasks pass. The notifications suite passes 30 tests, including mocked outbound delivery and all four sender-precedence cases. The delivery regression also covers channel selection and the default recipient, replacing a duplicate target-construction test. Full pre-push command output was captured locally.

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links (preview)	Ready	Visit Preview	Inspect	Sep 17, 2026 7:01am

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge; the final head correctly applies sender precedence and resolves both previous repository-rule findings.

Summary

This PR makes alarm notifications honor self-hosted sender configuration while preserving per-alarm overrides and hosted defaults.

• Resolves alarm senders through the existing ALERTS_EMAIL_FROM → EMAIL_FROM configuration fallback.
• Keeps non-empty per-destination sender overrides at the highest precedence.
• Adds the environment package dependency and forwards both sender variables through Turbo.
• Updates the example environment configuration and adds delivery-level regression coverage for sender precedence.
• Replaces the loop and prohibited delete operator identified in the previous review with parameterized tests and Reflect.deleteProperty.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Build alarm email target] --> B{Non-empty destination from?}
    B -- Yes --> C[Use destination override]
    B -- No --> D{ALERTS_EMAIL_FROM configured?}
    D -- Yes --> E[Use alert-specific sender]
    D -- No --> F[Use EMAIL_FROM fallback]
    C --> G[Send through Resend]
    E --> G
    F --> G

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_{Reviews (2) · Last reviewed commit: "test(api): isolate alarm sender regressi..."}

[izadoesdev]

@greptileai review this. The two test-style findings are fixed in f27025c; please review the final head.