#40 wiki discard: bless rm + git in docs; never-delete covers entities only

SOURCE: swarm friction #6 (verified: test wiki page removable only via plain rm; no verb; "never delete / archive only" feels violated). FIX: DOCS ONLY — clarify the carve-out honestly: spec [wiki]: "wiki pages are plain files in git; edit or remove with rm + git (git is the undo log); 'never delete' governs ENTITY history (issues/prs/tasks), not doc files." One line in AGENTS.md too. NO new verb, no archive machinery for wiki (bitter lesson: docs were missing, not verbs). DONE: rm on wiki files is blessed on paper; entities still close/archive only.