ludic remove <module> and ludic get --json (R9)

remove is the inverse of add: the require line leaves package.ludic; the lock keeps exactly what the
remaining requires still reach, read from the store's copy of each locked package.ludic (no
network), so a package another still requires stays locked and what only the removed one brought in
leaves with it; each leaving package loses the ludic_modules/ symlink add made, never the shared
store entry. Refused (exit 1) when package.ludic does not require the module; source still
importing a removed package is a warning. With no store copy to read, only the named module leaves.

get --json diffs the lock before and after in memory and prints {added, removed, changed,
unchanged} on stdout (an entry as the lock records it: name, version, hash, kind, provides; a change
as name, from, to, from_hash, to_hash), the resolver's lines on stderr. Cases added to test-pkg,
not run.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -144,6 +144,7 @@ cached in a content-addressed store:
 ```bash
 ludic add git.workshopsoft.io/user/pkg   # resolve, fetch, link into ludic_modules/
 ludic get                                # install from package.ludic, write the lock
+ludic remove git.workshopsoft.io/user/pkg   # the inverse of add
 ludic verify                             # check locked packages against the store
 ```