ludic fmt for editors: --lint --json, and a buffer on stdin (R9)

ludic-fmt --lint --json prints the violations --lint reports as one JSON array on stdout,
[{file, line, col, rule, message}] ordered by file, line and column (col where the rule knows it),
the summary on stderr, --lint's exit status, and never rewrites the baseline. ludic-fmt - refuses a
buffer that does not read as Ludic (a string/template/key literal left open, a bracket never closed
or closed by the wrong one) with exit 2 and name:line:col on stderr; - --lint judges a buffer as the
file --stdin-name names (--stdin-rel: that path relative to the project), against its baseline and
lint paths. ludic fmt --lint and ludic fmt - run it from the nearest package.ludic upwards (from
--stdin-name's directory when given). Hooks read nothing and write to stderr under --json or -.
Regression cases added to test-tools and ludic-dev test (fmt_editor_cases), not run.

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

tools/ludic-cli/main.ludic

@@ -79,6 +79,9 @@ program Ludic {
     print("  upgrade [version]             reinstall from the docs site (the same script that installed it)")
     print("  doctor                        check that the install is complete and usable")
     print("  fmt [--check] [paths...]      format Ludic source in place (--check: report, write nothing)")
+    print("  fmt --lint [--json]           check the project's `lint` rules (--json: one JSON array on stdout)")
+    print("  fmt - [--stdin-name PATH]     format stdin to stdout under the project's rules, as if it were PATH")
+    print("  fmt - --lint [--json] [--stdin-name PATH]   lint stdin as PATH")
     print("  lsp                           run the language server on stdio (what editors spawn)")
     print("  ui-preview [--font DIR]       preview a game's ludic.ui components for a studio, on stdio")
     print("  help                          this message")