Convert the review domain to strict TypeScript #23

Outcome

Markover's pure review model is expressed with strict, behavior-preserving TypeScript contracts.

Stack position

2 of 7 — stacked on the TypeScript build foundation.

Acceptance criteria

• Tree parsing, settings, and source-edit modules are converted.
• Domain invariants use precise types and discriminated unions where they eliminate impossible states.
• Existing runtime normalization and validation behavior is preserved.
• Corresponding tests are converted in the same PR.
• No blanket any, @ts-ignore, or disabled type checking is introduced.
• The temporary JavaScript boundary shrinks and all checks pass.