docs(track-a): close protected TTY auth source task

[blakinio]

SUPERSEDED by fresh-current-main replacement PR #522 after main advanced through #521 while this PR was in Ready-state validation.

Historical exact head 665eeb549250173c1361c7aba1b79380ac9898e6 passed the lifecycle audit and both pre-ready/ready CI generations, but strict current-main freshness requires the closeout to be replayed from current main. Do not merge #520; #522 owns the lifecycle closeout.

[blakinio]

Fresh lifecycle-only audit on exact head 665eeb549250173c1361c7aba1b79380ac9898e6: PASS. The diff is exactly two task-lifecycle paths: delete the stale active #510 record and add its completed archive record. Verified load-bearing closeout facts against live PR #510 state/comments/workflow runs: implementation head 5c2a89e59d474d87faecae78bf1321c2d12dc2ff, merge 13c5939ef89900a0998d56d2bf625c3906c9a68e, promotion review 4959013629, exact-head protected-TTY/native-auth/governance/repository-CI runs all SUCCESS, and PR #475 release head 8bf26dde309c46f08be414c4d2aef3e3599d7f5a. No runtime/client/login/credential/bridge behavior changes, no secret material, no ownership expansion, and no open material finding. E2E: NOT_APPLICABLE for this lifecycle-only move.