Migrate to TypeScript and refactor components.

[thekeenant]

• Migrate everything to TS.
• Avoid 'any' and 'unknown'
• Prefer Redux Toolkit (slices + configureStore) to reduce boilerplate and co-locate logic.
• Enforce strict TypeScript across Redux (no any, strict compiler/lint rules).
• Use createAsyncThunk or RTK Query for async/server state where appropriate (optional per domain).
• Co-locate reducers, actions, selectors, and tests in a slice per domain.
• Remove legacy action-type enums and split action files as each domain is migrated.
• Require CI to run type-check, lint, and tests before merging.