[csd113]

Adds an administrator-only Software Updates task to the existing admin workspace, with official stable-release checks, persisted progress/recovery results and pre-upgrade snapshot metadata in Backups. Public readiness reports only the running package version. Containers and unsupported native deployments remain check-only.

Supported Linux deployments use a separate operator-provisioned updater, authenticated fixed-operation local IPC, signed bounded artifacts, complete verified snapshots and activation/migration/readiness rollback. Installation requires administrator reauthentication, CSRF/same-origin validation, explicit confirmation and expiring one-use approval. The updater executable and independently trusted public key remain operator-managed.

Includes the completed public posting/reading improvements on this branch and prepares package/changelog version 1.6.0. Release notes cover the actual history since published v1.5.0, including container, terminal, admin, public-interface and updater changes.

The independent audit covered all nine themes at 1280/390/320px, seven browser profiles, native/no-JavaScript forms, keyboard/dialog focus, authorization privacy, progress/failure/recovery and surrounding admin tasks. It fixes stale post-install availability notices and WebKit preferences focus after returning to desktop. Linux browser CI provides real virtual audio output; fixture corrections await completed redirects and isolate intentional session revocation while strengthening retained-session checks. Assertions, retries, timeouts and exclusions are preserved.

Validation

Final head: a51a7d57885c0ed542189fe1f4f345c6eec00b10.

• All five required native GitHub jobs and Dependency Audit passed; full Rust tests: 2,509 passed, none failed/ignored.
• All four full native Linux browser jobs passed: 795 passed, 489 conditional skips, zero unexpected failures (1,284 executions). Chromium:283/38; Firefox:173/148; WebKit:175/146; Chromium no-JavaScript:164/157.
• Final focused seven-profile UI run: 101 passed, four existing no-JavaScript enhancement skips, zero failures. Session-revocation repetitions: 21/21 across seven local profiles and 3/3 Linux Chromium, with strict diagnostics.
• Locked checks, strict Clippy, formatting, dependency policy, Rust 1.91/Linux strict lint and optimized both-binary builds passed. Offline packaging/signing 7/7, JavaScript/YAML, browser harness and whitespace checks passed.

Supplemental remote Linux browser tests explicitly retain their download-path/SOCKS adapter limitations; they are not substituted for the successful native GitHub runs. Live Linux/systemd privilege/service/reboot recovery needs disposable staging before production rollout. No production/self-update was triggered. Evidence and limitations are documented in docs/software-update-ui-release-audit.md.

Stable publication is held until the operator provisions RUSTCHAN_UPDATE_SIGNING_KEY. This PR prepares the source and complete changelog; it does not create or publish a v1.6.0 tag/release.