[Artifact Forest 8/9] Add a creative conversion toolchain profile and doctor surface

[szmyty]

Parent: #421
Coordinates with: #424, #425, #426, #427, #428

Outcome

Make the optional creative/script/transcript provider stack discoverable and reproducible without making every tool a global Renderflow dependency.

Candidate provider set

• scripttool
• Node.js + afterwriting
• Poppler/pdftotext
• Tesseract
• FFmpeg + FFprobe
• local speech-transcription provider/model

Deliverables

• Add stable tool/provider registry entries and capability IDs.
• Define an optional creative-publishing / equivalent doctor profile.
• Report installed/missing/incompatible tools independently.
• Document install strategy per supported platform and devcontainer where practical.
• Pin or record exact versions used by fixtures and releases.
• Separate executable licensing from model/font licensing.
• Ensure planner selects only available compatible providers.
• Produce machine-readable toolchain fingerprint for a full creative artifact forest.

Acceptance criteria

• Core Renderflow still works without optional creative providers.
• One doctor/capability command explains exactly which screenplay/transcript routes are available on the host.
• Missing one provider prunes only its capabilities rather than invalidating unrelated conversions.
• Tool/model/license evidence is represented without bundling incompatible software into Renderflow core.
• Devcontainer/local setup can reproduce the supported fixture toolchain where licensing permits.

Non-goals

A universal package manager or automatic installation of third-party binaries without user intent.