docs: captions, transcript-grounded authoring, and brand voice

[jdwit]

What

The docs site guides had drifted behind the shipped CLI. Caption/transcript reads, the transcript-grounded metadata authoring loop, and per-channel brand voice were documented only in the bundled agent skill (SKILL.md), not on the site. This brings the site (and README/index) up to parity.

The commands themselves already live on main; this is docs-only.

Changes

• docs/videos.md: new Captions and transcripts section (videos captions, videos transcript, track kinds, --lang, restricted-ASR fallback) and Authoring metadata section (the transcript-grounded, on-brand loop with the brand-for-tone / transcript-for-claims rules).
• docs/profiles.md: new Brand voice section (profile brand show/set/edit, --profile, template seeding, 0600 storage) and brand.md added to the storage tree.
• docs/api-quota.md: captions.list (50) and captions.download (200) rows, plus a note that videos transcript spends ~250 units (list + download).
• docs/index.md and README.md: surface the caption/transcript/brand-voice capability, framed as inputs the CLI supplies rather than copy it generates (consistent with the authoring section).
• mkdocs.yml: note authoring in the Videos nav label.

Verification

• mkdocs build --strict passes (cross-page anchors resolve).
• pytest green (338 passed).
• Every factual claim (command names, flags, quota numbers, storage paths, dry-run behavior, anchor targets) fact-checked against the source; one overstatement in the README/index highlights was corrected.
• ASCII-only; no em/en dashes or smart quotes introduced.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.03%. Comparing base (d8342b4) to head (90dff8d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #54   +/-   ##
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  Coverage   85.03%   85.03%           
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  Files          15       15           
  Lines        2660     2660           
  Branches      393      393           
=======================================
  Hits         2262     2262           
  Misses        264      264           
  Partials      134      134           

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