fix(core,producer): composition CSS variables reach the render path at eval time

Live testing of the compile-time variable emission surfaced four gaps:

- The producer render path never emitted the compile-time stylesheet (only
  the preview bundler did), so eval-time reads — GSAP .from immediateRender,
  top-level getComputedStyle — saw undefined vars in rendered output. The
  producer's inlineSubCompositions now calls the shared
  emitRootCompositionVariableStyles and passes the variable hooks.
- --variables overrides weren't visible at eval time. They now thread from
  the orchestrator / distributed plan through compileStage into the emitted
  rules (window.__hfVariables still covers script reads).
- Per-declarer rules anchored on data-composition-id, which two inlined
  instances of one sub-composition share — instance A's rule restyled
  instance B, and a rule directly on the declarer defeated the host's
  inherited data-variable-values. Rules now anchor on per-instance
  data-hf-var-scope markers and layer nearest-host values over declared
  defaults, mirroring the runtime loader.
- Emission ignored authored CSS; a declared default now yields to a var
  already defined in an authored <style> block (define-if-absent, matching
  the runtime injection).

Also: the figma importer emits background-color (longhand) for solid fills.
GSAP backgroundColor tweens cannot read a var() through the background
shorthand — its pending-substitution longhands serialize empty, so .from
captured nothing and settled on transparent (pre-existing GSAP interaction,
reproduced with no composition variables involved).

Validated live: eval-time default + override, .from + override, two-instance
host branding, authored :root precedence, SDS brand-loop pixel parity.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packages/cli/src/commands/figma/component.test.ts

@@ -74,7 +74,7 @@ describe("runComponentImport", () => {
 
   it("bakes literals and reports unresolved bindings when the index is empty", async () => {
     const { out, html } = await importHero();
-    expect(html).toContain("background: #0066FF");
+    expect(html).toContain("background-color: #0066FF");
     expect(html).not.toContain("var(");
     expect(out.unresolved).toHaveLength(1);
     expect(out.unresolved[0]?.figmaId).toBe("VariableID:1:1");