feat(lessc): wire compress, source maps, URL rewriting, and math CLI flags

[matthew-dean]

The less.render() API already supports compress, source maps (including the
rootpath/basepath/url path variants and inline data URIs), URL rewriting,
and math modes — but lessc rejected all of those flags and pointed users at
the API. This forwards them from the CLI so files can be compiled with the same
surface as the programmatic API.

New / changed flags

• --compress / -x
• --math=<always|parens-division|parens>
• --rewrite-urls[=all|local|off], --rootpath=<path>, --url-args=<args>
• --source-map[=file] — writes the sidecar .map next to the output and
  annotates the CSS with its basename; --source-map-inline embeds a base64
  data URI instead of writing a file
• --source-map-include-source, --source-map-rootpath, --source-map-basepath,
  --source-map-url for the path variants
• --collapse-nesting now also accepts =native|compact

The source-map engine already honors rootpath/basepath/url and sets the map's
file field, so no engine change was needed — this exposes and tests them
through the CLI. When source maps are requested but CSS goes to stdout (no output
file for a sidecar), the map is inlined.

Tests / docs

• test/lessc-alpha.mjs gains positive coverage for every new flag: compress,
  math, url-args, rootpath, --source-map (sidecar .map shape + file field +
  sources), --source-map-inline (data URI, no sidecar), and the
  basepath/rootpath/include-source/url path variants.
• The help text and V5-STATUS.md are updated: the CLI-flags row and the
  source-map path-variant note both move from "in progress" to supported.

Full test:alpha (typecheck, build, lessc, support, source-maps, fixtures),
publish-dry-run, and the packed-consumer proof pass locally.

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[greptile-apps]

Confidence Score: 4/5

The PR should not merge until explicit source-map files outside the CSS directory produce an annotation that resolves to the sidecar actually written.

Summary

This PR exposes existing render functionality through the alpha lessc CLI.

• Adds compression, math, URL-rewriting, source-map, and expanded nesting flags.
• Writes source-map sidecars or embeds inline maps as appropriate.
• Updates CLI help, status documentation, and end-to-end CLI coverage.
• Explicit source-map paths in directories other than the CSS directory currently produce an annotation pointing to the wrong location.

_{Reviews (1) · Last reviewed commit: "feat(lessc): wire compress, source maps,..."}