S6: catalog inspection — relix catalog files/ls/schema/where #10

Part of #17. Design: docs/design.md §5.3.

Scope

• relix catalog files: every file loaded, in order, with the names each declared and whether it was trusted.
• relix catalog ls: name, kind, arity and defining file.
• relix catalog schema NAME: columns and types.
• relix catalog where NAME: the declaration that won and the ones it shadowed.

ls and schema are queries over the engine's introspection relations (relix.relations, relix.columns), rendered through the S2 row renderers, so they come out as TSV or NDJSON in a pipe.

Dependencies

• S2 (S2: output — isatty defaults, last-query rule, assertions, EPIPE/SIGINT discipline #6), S4 (S4: catalog discovery — .relix/ directories up the hierarchy, nearest-wins overlay #8), S5 (S5: catalog trust — direnv-style trust for project .relix/ directories #9).

Acceptance

• Each subcommand over a multi-level fixture tree, in table and tsv.
• where reports shadowed declarations.
• schema on an unknown name exits 3.