Make this fourth and final planned set of changes to the same Device Lifecycle Hub app. Preserve the real read-only Office 365 Users Profile integration, every original/saved request and line, activity/approval history, assets and theme/preferences. Do not reset/reseed, replace the app, add real business connectors or send anything.

1. Change the finance approval threshold from GBP 1,000 to GBP 1,440: newly manager-approved requests above 1,440 need finance; exactly 1,440 or below go directly to Approved. Do not retroactively change requests already approved, fulfilled, rejected or awaiting finance.
2. Add a manager "Request changes" action for Pending manager requests, requiring a nonblank reason. It returns the request to Draft with an activity/history entry, preserves its ID/lines and lets its original requester edit and resubmit it. Resubmission retains history and re-enters Pending manager. Add requester Cancel for their own Draft or Pending manager request, requiring confirmation. Cancelled is terminal and must not alter stock. Managers/finance cannot act on cancelled requests.
3. Add a required Cost centre field to new/draft request forms: CC100 for Engineering and CC200 for Operations. Set the appropriate value from the saved request's department when migrating old records without losing any other fields. Save it with the request and show it in details/approval views. Validate a department/cost-centre mismatch explicitly.
4. Add "Low stock" to Overview and Catalogue for availability of two units or fewer, including zero. Initially, before any fulfilment, three device models qualify. Overview's low-stock tile opens that filtered Catalogue. Add text search by request ID/justification and combined status filtering in My requests; Clear filters restores the selected persona's requests.
5. Make the complete seven-screen experience usable at both wide desktop and 390px mobile widths. Keep request lines, totals, action controls, approval comments, asset forms, Profile and preference controls readable and reachable without page-wide horizontal scrolling or squeezed unusable inputs. Preserve explicit light/dark switching and visible keyboard focus.

These are planned product changes, not a request for self-review. Implement them without a separate acceptance-testing/audit pass or extra test records; independent review is performed outside Cowork. Briefly summarize the changes and actual limitations.