test: Inline unit tests for server.rs, alert.rs, auth.rs, config.rs (0 inline tests)

[ajianaz]

What

Add inline unit tests for trapfalld/src/server.rs (1045 LOC) and related handler files that currently have zero inline tests.

Why

BMAD COO finding: TrapFall has 231 tests total, but they're concentrated in trapfall-db (81) and integration-level tests/ directories. The HTTP handler layer — server.rs (1045 LOC), alert.rs (266 LOC), auth.rs (312 LOC), config.rs (281 LOC) — has zero inline #[test] functions.

This means handler-level edge cases (malformed requests, auth edge cases, rate limiting behavior) are only caught by E2E tests, which are slower and less precise.

Changes

1. server.rs: Unit tests for:
   • Request routing (each endpoint returns correct status for valid/invalid input)
   • Error response shapes
   • Authentication middleware (valid token, expired token, missing token, malformed token)
   • Rate limiting behavior
2. alert.rs: Unit tests for:
   • Rule matching logic (condition evaluation)
   • Cooldown tracking
   • Webhook dispatch (mock HTTP)
3. auth.rs: Unit tests for:
   • JWT generation and validation
   • Argon2 password hashing/verification
   • DSN validation against registered projects
4. config.rs: Unit tests for:
   • Default values
   • Environment variable parsing
   • Invalid config handling

Testing

This IS the testing task. Success = cargo test --workspace count increases by 30-50 tests, with handler-level coverage significantly improved.

[ajianaz]

Implemented in PR #305 (branch refactor/v0.3.0-ghost-crates). See commit history for details.