feat(cli): add --composition flag to render specific compositions (#631)

* feat(cli): add --composition flag to render specific compositions

Expose the existing entryFile config in the producer through
a new --composition / -c CLI flag. This lets users render
individual composition files without restructuring their project:

  hyperframes render -c compositions/intro.html -o intro.mp4

The flag validates the file exists before starting the render,
threads through both local and Docker render paths, and is
documented in the CLI help, examples, and docs.

* fix(cli): address PR review — path traversal guard, forward tests, tripwire

- Add path-containment check mirroring hyperframeLint.ts: reject
  --composition paths that escape the project directory
- Normalize leading ./ from composition paths for clean render plan output
- Improve error message: suggest .html file path instead of compositions command
- Add description note about <template> sub-composition constraint
- Add render.test.ts: entryFile forwarded to createRenderJob (forward + omit)
- Update dockerRunArgs tripwire test with entryFile coverage

packages/cli/src/utils/dockerRunArgs.ts

@@ -30,6 +30,7 @@ export interface DockerRenderOptions {
   videoBitrate?: string;
   quiet: boolean;
   variables?: Record<string, unknown>;
+  entryFile?: string;
 }
 
 export function buildDockerRunArgs(input: DockerRunArgsInput): string[] {
@@ -67,5 +68,6 @@ export function buildDockerRunArgs(input: DockerRunArgsInput): string[] {
     ...(options.variables && Object.keys(options.variables).length > 0
       ? ["--variables", JSON.stringify(options.variables)]
       : []),
+    ...(options.entryFile ? ["--composition", options.entryFile] : []),
   ];
 }