fix(core,cli): address PR review — consistent 403 error shape, cap Retry-After, URL-safe ref split

Rames's inline findings on #2112:
- forbiddenError now RETURNS in every branch (BAD_TOKEN no longer throws
  inside) so the caller's single throw covers all cases — no mixed
  throw/return contract for a future wrapping caller.
- retryAfterMs capped at 60s: a spec-legal Retry-After: 3600 no longer
  silently blocks the CLI for an hour before RATE_LIMITED.
- asset ref gathering extracted to gatherAssetRefs() and made URL-safe:
  bare fileKey:nodeId tokens comma-split, but a figma URL with commas in
  its query (multi-select node-id=1:2,3:4) is kept whole.
- Documented in SKILL that 429 retry lives in the shared request path, so
  EVERY read endpoint retries (not just asset) — blast-radius note the
  reviewer asked for. variables intentionally still retries: its fallback
  is REQUIRES_ENTERPRISE-only, and a 429 there is transient, not a gate.

Tests: retry-cap (3600→60000), non-styles endpoint retry, gatherAssetRefs
URL-vs-bare split. client 24, cli asset 11.

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

packages/core/src/figma/client.test.ts

@@ -153,6 +153,47 @@ describe("error mapping", () => {
     expect(waits).toEqual([1000, 2000]); // exponential backoff
   });
 
+  it("caps an oversized Retry-After at 60s so the CLI can't block for an hour", async () => {
+    let n = 0;
+    const waits: number[] = [];
+    const client = createFigmaClient({
+      token: "t",
+      fetch: (() => {
+        n += 1;
+        return Promise.resolve(
+          n === 1
+            ? new Response("{}", { status: 429, headers: { "retry-after": "3600" } })
+            : jsonResponse(200, { meta: { styles: [] } }),
+        );
+      }) as FigmaFetch,
+      sleep: (ms) => {
+        waits.push(ms);
+        return Promise.resolve();
+      },
+    });
+    await client.styles("F");
+    expect(waits).toEqual([60_000]); // 3600s clamped, not 3_600_000
+  });
+
+  it("retries 429 on non-styles endpoints too (retry lives in the shared get)", async () => {
+    let n = 0;
+    const client = createFigmaClient({
+      token: "t",
+      fetch: (() => {
+        n += 1;
+        return Promise.resolve(
+          n < 2
+            ? jsonResponse(429, {})
+            : jsonResponse(200, { images: { "1:2": "https://cdn/a.png" } }),
+        );
+      }) as FigmaFetch,
+      sleep: () => Promise.resolve(),
+    });
+    const out = await client.renderNodes("F", ["1:2"], { format: "png" });
+    expect(out[0]?.url).toBe("https://cdn/a.png");
+    expect(n).toBe(2); // one 429 then success
+  });
+
   it("honors Retry-After (seconds) over the backoff default", async () => {
     let n = 0;
     const waits: number[] = [];