monopam/lint: stop hiding sibling missing deps; declare them
Treating sibling packages in the same subtree as automatically present
masked real opam-side gaps: \`dune build -p X\` only sees X's depends,
so a sibling used as a library must still be declared. With the filter
removed, lint surfaces three real cases:
- ocaml-did: did.resolve uses did-web/did-plc but did.opam didn't say so
- ocaml-atp: tangled/bsky/standard-site libs use xrpc-auth and tangled
also uses atp-lexicon-atproto, none declared
- ocaml-requests: ocurl exec uses nox-tty/vlog (only surfaced now that
the previous commit attributes (executables ...) deps to a package)
Each of those depends gets the missing entry.