Release v1.0.12

[RomeoCavazza]

Summary

Release the completed Alertmanager lifecycle contract already merged and green on main.

• bump every server, web and desktop manifest/lockfile to 1.0.12;
• document per-alert firing/resolved handling and semantic idempotency;
• document bounded Alertmanager delivery metrics and the official-container E2E proof.

Validation

• ./tooling/verify_release_version.sh 1.0.12
• cargo fmt --all --check
• SQLX_OFFLINE=true DATABASE_URL=postgres://opswarden:opswarden@127.0.0.1:5433/opswarden cargo test --workspace — green
• npm run lint --workspace client-web
• npm run typecheck --workspace client-web
• npm run test:coverage --workspace client-web — 211 tests, 72.31% lines
• ./tooling/check_source_hygiene.sh origin/main

Clippy is delegated to the required CI gate because the local Rust installation does not include the Clippy component.

Release discipline

No tag is created or pushed by this PR. v1.0.12 will be annotated only after this commit is merged into main and the post-merge required gate is green.