Shared gh-style conveniences: --json/--jq, TTY tables, --web, prompts #28

Cross-cutting behaviour every command group uses. Land it alongside the first dedicated command (likely auth status or product).

• --json <fields> and --jq <expr> on every read; a table when stdout is a TTY.
• --web opens the matching source.coop page.
• account/product shorthand, e.g. source-coop product view radiant/landcover.
• Interactive prompts for missing required arguments when a TTY is attached; none otherwise (fail with a usage error).
• --help text and any generated request types come from the published OpenAPI document at source.coop/api/openapi.

Part of #21. Per the epic, the CLI validates nothing itself: it sends the request and shows the API's field_errors. Add a CLI path to docs.source.coop docs/using-source/ wherever this flow gets one.