docs(cli): explain FFmpeg setup without a package manager

[user-github-me]

When FFmpeg is missing on a Mac without Homebrew, the CLI skill's troubleshooting reference offers no usable setup path even though HyperFrames already supports configured binaries. Document both HYPERFRAMES_FFMPEG_PATH / HYPERFRAMES_FFPROBE_PATH and project-local .hyperframes/bin, including their discovery precedence and Windows filenames.

Add a copyable doctor --json check for the two encoding dependencies. The report also includes optional tools, so checking only its overall ok can reject a working local encoding setup.

Refs #5232. This covers the existing-binary setup documentation; the issue's early workflow preflight and CLI hint proposals remain follow-up work.

Validation: built CLI exercised in seven cases (explicit paths, project-local binaries, both precedence controls, and each/both missing overrides), plus two incomplete-report controls. The documented jq check accepted all four working setups and rejected all missing setups. Root lint, skill cross-references, formatting, comment checks, and commit hooks passed. Confirmed the official FFmpeg download page provides macOS builds. No product behavior or dependencies change.

[jrusso1020]

Thanks, this fills a real gap for machines without Homebrew. I checked the documented behavior against the binary resolver and doctor:

• the env overrides take precedence;
• PATH is checked before .hyperframes/bin;
• a configured path that doesn't exist is reported as missing;
• the FFmpeg and FFprobe entries carry the resolved path.

The jq gate is a sensible way to avoid failing on optional tools.

— Rames