refactor: DELETE trapfall-alert ghost crate (3 LOC stub)

[ajianaz]

What

Delete trapfall-alert crate (3 LOC stub containing only // TODO: Phase 0 — scaffold only).

Why

BMAD COO finding: The alert engine is fully implemented in trapfalld/src/alert.rs (266 LOC) — webhook dispatch, cooldown logic, rule matching, alert history. The standalone trapfall-alert crate contributes nothing. It's pulled into trapfalld's Cargo.toml but adds zero code. This is organizational fiction that misleads contributors about where alerting logic lives.

Impact: Contributors seeing trapfall-alert expect to find alert logic there. They won't. This creates onboarding friction and maintenance overhead (extra Cargo.toml, dependency declarations, workspace member).

Changes

1. Remove trapfall-alert/ directory entirely
2. Remove "crates/trapfall-alert" from root Cargo.toml workspace members
3. Remove trapfall-alert dependency from trapfalld/Cargo.toml
4. If any re-exports reference the crate, move them to trapfalld/src/lib.rs or wherever appropriate
5. Verify cargo build --workspace passes
6. Verify cargo test --workspace passes

Testing

• cargo build --workspace — must pass
• cargo test --workspace — all 231 tests must still pass
• cargo clippy --workspace --all-targets -- -D warnings — clean
• Verify alert functionality still works (webhook dispatch, cooldowns, rule matching)