feat(cli): accept ffmpeg-style rational fps (NTSC, PAL, slow-mo)

Replaces the rigid `--fps 24|30|60` whitelist with a numeric range and
adds support for ffmpeg-style fractional framerates so NTSC stays exact
end-to-end.

- `--fps 30` keeps working (integer fps)
- `--fps 30000/1001` now means exact NTSC 29.97 (not the lossy decimal)
- `--fps 24000/1001`, `--fps 60000/1001`, `--fps 25/50/120/240` all work
- Decimals like `--fps 29.97` are rejected with a friendly error pointing
  the user at the rational form, since `29.97` and `30000/1001` round
  to different framerates inside ffmpeg

Carries an `Fps = { num: number; den: number }` rational end-to-end:
RenderConfig, EncoderOptions, StreamingEncoderOptions, CaptureOptions,
DockerRenderOptions, Studio API request body, regression-harness
meta.json. The `-r` and `-framerate` ffmpeg args emit the rational form
verbatim (`30000/1001`) so no decimal round-trip happens at the encoder
boundary. Frame-interval math uses `1000 * den / num` ms (33.366… for
NTSC, 33.333… for integer 30).

Helpers live in @hyperframes/core:
- `parseFps(input: string | number): FpsParseResult` — discriminated
  parser used by both the CLI and the Studio API route
- `fpsToFfmpegArg(fps: Fps): string` — emits "30" or "30000/1001"
- `fpsToNumber(fps: Fps): number` — for arithmetic (telemetry, frame
  count, frame-index → time)

Studio API wire format accepts polymorphic `fps: number | string`:
- number → integer fps (`30`)
- string → rational (`"30000/1001"`)
Decimals are rejected; matches the same rule as the CLI.

Existing meta.json fixtures with integer `"fps": 30` continue to load
unchanged — the regression-harness validator now normalizes both number
and string inputs through `parseFps`.

packages/cli/src/utils/dockerRunArgs.test.ts

@@ -2,7 +2,7 @@ import { describe, expect, it } from "vitest";
 import { buildDockerRunArgs, type DockerRenderOptions } from "./dockerRunArgs.js";
 
 const BASE: DockerRenderOptions = {
-  fps: 30,
+  fps: { num: 30, den: 1 },
   quality: "standard",
   format: "mp4",
   gpu: false,
@@ -151,7 +151,7 @@ describe("buildDockerRunArgs", () => {
     const args = buildDockerRunArgs({
       ...FIXED_INPUT,
       options: {
-        fps: 60,
+        fps: { num: 60, den: 1 },
         quality: "high",
         format: "webm",
         workers: 8,
@@ -240,6 +240,29 @@ describe("buildDockerRunArgs", () => {
     expect(args).not.toContain("--composition");
   });
 
+  it("forwards rational --fps verbatim (NTSC 30000/1001)", () => {
+    // Regression for the fps fraction-syntax feature: the rational form must
+    // survive the host → container hop as a single `30000/1001` argument so
+    // the in-container CLI re-parses it as exact NTSC, not 29.97 decimal.
+    const args = buildDockerRunArgs({
+      ...FIXED_INPUT,
+      options: { ...BASE, fps: { num: 30000, den: 1001 } },
+    });
+    const fpsIdx = args.indexOf("--fps");
+    expect(fpsIdx).toBeGreaterThanOrEqual(0);
+    expect(args[fpsIdx + 1]).toBe("30000/1001");
+  });
+
+  it("forwards integer --fps as a bare integer string", () => {
+    const args = buildDockerRunArgs({
+      ...FIXED_INPUT,
+      options: { ...BASE, fps: { num: 60, den: 1 } },
+    });
+    const fpsIdx = args.indexOf("--fps");
+    expect(fpsIdx).toBeGreaterThanOrEqual(0);
+    expect(args[fpsIdx + 1]).toBe("60");
+  });
+
   it("forwards --resolution to the container when outputResolution is set", () => {
     const args = buildDockerRunArgs({
       ...FIXED_INPUT,