build(dotnet): lock SDK and packages

Pin the SDK feature band and commit transitive NuGet content hashes so CI fails on unreviewed dependency drift.

docs/work-programmes/master-progress.md

@@ -41,6 +41,7 @@ Updated: 2026-08-30
 - Localized the pre-authentication security-check label and the embedded Turnstile challenge language, so switching to Bokmål no longer leaves the verification widget in English.
 - Localized the remaining active helper defaults in the admin SMTP test form, pasted-email importer, and image-crop alternative text.
 - Restored the local Python 3.12 toolchain and both virtual environments; the AI sidecar now passes 26/26 tests. Added a Next.js-compatible ESLint 9 flat configuration, strict zero-warning scripts, and a patched CommonJS-compatible `brace-expansion` override. The lint gate passes with zero findings and npm audit reports zero vulnerabilities.
+- Pinned the repository to .NET SDK 9.0.317, generated content-hashed transitive NuGet locks for the API and test project, and made CI restores fail on lock drift. Locked restore and backend 719/719 pass; the current NuGet graph has no known vulnerable packages.
 
 ### In progress
 
@@ -109,7 +110,7 @@ Updated: 2026-08-30
 - Manual desktop browser review: webpack development server rendered the new Career navigation and Overview correctly in dark mode; API-dependent profile status remained unavailable because the backend was not running for that isolated UI review.
 
 - **Overall programme status:** Active but externally blocked. Eight packages are locally verified and twenty-seven are implemented with verification incomplete. The prioritized admin-only version indicator, every immediate repository/browser item, SEC-006/SEC-007 repository boundaries, SEC-009, the PROD-001 read-only inventory, and the PROD-003 safe benchmark harness are complete on the feature branch.
-- **Current work package:** Reconcile the next safe repository item while SEC-006/SEC-007 await Linux image/runtime proof.
+- **Current work package:** JT-017/JT-018 supply-chain and developer-documentation hardening while external runtime gates remain blocked.
 - **Completed work packages:** None are `DONE`; all repository security/AI packages still have applicable browser, provider and/or production gates.
 - **Locally verified work:** SEC-001, SEC-002, SEC-003, SEC-005A, CORE-001, PROD-002, DEP-001 and VER-001 (`VERIFIED LOCALLY`).
 - **Implemented, verification incomplete:** SEC-004, SEC-005B, SEC-006, SEC-007, SEC-008, SEC-009, CORE-002, BG-001, OPS-001A/B/C, POL-001/002, AI-001/002/003/004, UX-001/002/003, QA-001, CAREER-001/002, MAIL-001, JOBS-001/002 and PRODUCT-001 (`IMPLEMENTED — NOT VERIFIED`). Their safe repository/browser scope is implemented; production/native-device/provider/retention gates remain where recorded.