Observer 0.5.0a13: read cache and timed watches

Adds a pure local Service 2 ReadCache and timed local/Mesh human watches, with independent component expiry, unchanged activity age and conservative revocation. API 2, snapshot/watch 4, Service 2 and frozen Mesh Agent profile 1 remain unchanged.

Exact wheel: 646a067dcba3b1a37354c01b9aa91a247351adabbb352b19f732bd6f89cedbcc. Production source revision: 4cb6233. Both-host installed/native acceptance and reader-only rollback/reselection pass; 425 optional-Mesh source checks and 67 installed checks per host pass. Six existing synthetic fixtures were made UID-portable in a following test-only commit.

Snap and Starship select the read CLI only. The a11 collector, a16 writer and existing a4 bridge remain independently selected without restart. Sustained ordinary-host measurements identify material collector retention-scan and fleet-reader costs for separate follow-ups. Claude partial registration scope, unsupported background workflows and older Codex history limits remain explicit. No frontend, notification/event, provider-policy or action rollout is included.