Fix endpoint mobility across LAN and Tailscale

[papi-ux]

Summary

• remember bounded, deduplicated verified host endpoints so one computer can move between LAN and Tailscale routes without being re-added
• preserve UUID and exact certificate identity while retrying remembered candidates; allow plaintext fallback only for a real HTTP 401
• migrate current and legacy computer databases transactionally, skipping malformed sibling rows while preserving source databases on read or destination-write failure

Verification

• RootDebug JVM: 855 tests, 0 failures, 0 skipped
• NonRoot_gameDebug JVM: 849 tests, 0 failures, 0 skipped
• RootDebug and NonRoot_gameDebug fail-on-error lint: passed
• RootDebug androidTest Kotlin compilation: passed
• focused post-commit identity/persistence tests: 57 passed
• compiling mutation campaign: 44/44 killed, 0 survivors/harness errors, production bytes restored
• immutable review of staged binary diff e4e12888965228e40ec2c9338a1dac47ec9b2133ae66b4f6716bb83e5ecc37d2: no actionable blockers
• arm64 NonRoot_game debug APK built reproducibly: a22d6e2b15c52c71d456aac51adbb8f44a5db5e6aa8d87c6301ab67d843ff0c1

Pending field gate

• install the exact commit APK on Retroid and re-run LAN → Tailscale → app restart → LAN failback with installed-APK pullback hash and full device/host restoration

The earlier field run predates the final hostname-chain and legacy-v1 hardening changes, so it is intentionally not counted for this commit.

Closes #144