Frontend Type-Safety Hardening: Clean TypeScript Build Across the App

A large internal code-quality batch promoted to QA that eliminates the frontend's accumulated TypeScript type errors (baseline ~205, driven to a clean typecheck). This is primarily a stability and maintainability investment touching ~100 files across Inbox, Mail, Documents, Batches, Resolution Center, and Admin Hub, with no intended change to existing user-facing behavior aside from one screen now reading live data.

The frontend had drifted from the backend API contract, accumulating roughly 205 TypeScript typecheck errors and a number of any/@ts-expect-error escape hatches. That gap let real defects (wrong property paths, unsafe null access, inconsistent pagination shapes) slip through unnoticed and blocked enabling strict type checking in CI. This batch closes the gap so the compiler can catch these classes of bugs before they reach users.

For clients, the visible product is largely unchanged; the benefit is reliability. Fixing unsafe property access and null handling reduces the chance of blank fields or runtime crashes in mail, document, batch, and resolution screens. One concrete behavior change: the mail Activity Log now displays real activity data from the API instead of placeholder/mock content. The team also recorded backend data gaps (e.g. missing assigned_on and status_name fields) for follow-up.

Promotion of the dev type-hardening initiative to qa (+6552/-2899 across ~100 files). Notable changes grounded in the diff:

• Aligned frontend types to actual API response shapes (e.g. nested paths creation_details.date, creation_details.username, file_details.file_name/file_url).
• Introduced reusable type guards (isSuccessResponse) and a generic PaginatedResponse<T> to standardize list/pagination handling.
• Hardened data-grid column typing (ColumnDef) across Inbox, Mail, Documents, Batches, Admin Hub (Folders, Organization, Rules, Document Types).
• Reworked Zustand mailOverview.store.ts (+216/-67) typing for the middleware chain and save payload.
• Replaced mock data with the live useGetMailActivity API in ActivityLogTab.
• Removed a @ts-expect-error in next.config.ts; restored next-env.d.ts and stopped git-ignoring it.
• Added docs/BACKEND_API_ANOMALIES.md documenting fields the FE expects but the API lacks; deleted two obsolete planning docs.

Risk is broad-surface but mostly low-depth: ~100 files touched, but the majority are type annotations, type guards, and assertions rather than logic rewrites. Main risks are (1) a mistyped property path or type assertion masking a real data mismatch, and (2) the ActivityLog live-data swap surfacing missing/oddly-shaped backend fields. Mitigation: changes were staged in sequential phases with a clean typecheck gate, and known backend gaps are tracked in BACKEND_API_ANOMALIES.md. Recommend a focused QA pass on the highest-churn screens before promotion to production.

• Smoke-test high-churn grids for correct columns, sorting, and pagination: Inbox, Mail, Documents, Batches, and Admin Hub (Folders, Organization, Rules, Document Types).
• Open mail and document detail/overview screens; confirm sender, file name, dates, and status render (no blanks or crashes).
• Verify the mail Activity Log now shows real activity entries and timestamps, not placeholder data.
• Exercise Resolution Center: mail/document resolution tabs, bulk status update, and assign/reassign flows.
• Confirm bulk actions (e.g. bulk delete organization, bulk assign) still complete and show result modals.
• Sanity-check that a fresh build/dev run starts cleanly (next-env.d.ts restored, code inspector plugin in dev).