fix: declare required-reason system uptime usage

[jlipworth]

Summary

• Add SystemBootTime / 35F9.1 to the shared privacy manifest; no runtime or playback changes.
• Audit all production uptime uses, including PMSKit retry timers, local raw baselines and exported in-app intervals against Apple's off-device exception.
• Add source/four-product packaging regression checks and narrow development/release guidance.

Refs #326 (intentionally not auto-closing: signed archive acceptance remains open). #325 collection/review-demo disclosure work is separate; no App Store Connect answers or policy changes are included.

Verification

• Canonical hermetic PMSKit: 121 XCTest + 1,707 Swift Testing tests passed; no live probes/media transcodes.
• Four privacy regression tests; strict MkDocs, rendered links, Mermaid and repository hygiene passed.
• Clean unsigned Release builds: visionOS Simulator, iOS Simulator, tvOS Simulator, arm64 macOS. Fresh executable mtimes verified.
• All four actual app manifests match source; each product includes the expected Crypto dependency manifest (empty required-API/collection arrays, tracking false). Packaging checker validates platform identity and nested plist readability.
• Passive iPhone Release install/launch: installed UUID matched, process alive, expected unauthenticated screen visually inspected, no fatal/assertion/uncaught-exception markers. Owned simulator shut down/deleted; no staged Mac app remains.

Remaining gates / limits

• Exact signed Release archive manifests and Xcode aggregate privacy reports for all four platforms are not verified. Unsigned packaged resources are not archive/signing validation. Keep Privacy manifest: declare production systemUptime API use #326 open until this acceptance item is satisfied.
• Native affected matrix conservatively selects hosted/UI lanes as well; those broad suites were not run for this resource-only fix. No visionOS launch claimed (main golden simulator-id file unavailable); no Mac launch claimed. No hardware/live-backend acceptance implied.
• No signing/account/server changes, archive upload, version bump, tag, merge or issue closure.

Sanitized data-flow and validation evidence: docs/evidence/2026-09-15-privacy-uptime-audit.md. Private build/log/screenshot artifacts are not published.

[jlipworth]

CI completed for 57014b10: all five reported checks are green (PR docs/hygiene/PMSKit and push hygiene/PMSKit). Local four-platform unsigned Release packaging, hermetic tests, strict documentation/hygiene and passive iPhone launch evidence are recorded in the PR audit. The exact signed Release archive + Xcode aggregate privacy-report gate remains open; this PR has not been merged and #326 remains open.