馃尶 Collaborative wiki on ATProto

Open wiki mode M2: access + submission path master

- canSubmitContribution(access): non-contributor on a public, open wiki - context exposes canSubmitContribution; /new + /edit allow contribution mode - createNoteAction/editNoteAction route non-contributor submissions to pending_contributions (write note+revision to PDS, envelope as wiki.lichen.contribution strongRefs) instead of going live - writeContributionRecord (PDS) + insertPendingContribution (DB) + COLLECTIONS - solo (no-collab) editor for contribution edits; tests for create path