feat: establish first-class provider adapter packs

[szmyty]

Closes #362

Summary

• add the versioned renderflow.adapter-catalog/v1 provider-pack contract and JSON Schema
• describe provider capabilities, media I/O, determinism, locality, fidelity, bounded execution, configuration, validation, provenance, maturity, and selection priority
• add a public deterministic provider selector with explicit preference ordering and complete fallback decisions
• catalog integrated Pandoc, Tectonic, and FFmpeg paths plus experimental ZIP, img2pdf, Ghostscript, Upscayl, jq, Tesseract, ImageMagick, and wkhtmltopdf packs
• add an inspectable adopt/adapt/reject/defer matrix across document, PDF, image, media, ebook, office, archive, data, OCR, and subtitle tool classes
• add renderflow tools ecosystem with JSON/YAML/text, capability filtering, live availability, explicit preferences, and available-only output
• register experimental jq, Tesseract, and ImageMagick tools without falsely adding executable graph edges
• fix FFmpeg discovery to use its supported -version probe
• add generated tool-registry updates and adapter-authoring documentation

Experimental catalog entries remain discoverable but do not become executable capabilities until an artifact-native edge/executor and validation evidence are registered.

Verification

• cargo check --workspace --all-targets
• full catalog JSON smoke: 11 provider contracts and 13 adoption evaluations
• capability-filtered OCR availability smoke
• explicit ImageMagick preference → unavailable decision → deterministic FFmpeg fallback smoke
• adapter schema JSON parse and catalog invariant checks
• git diff --check

Broad test/CI expansion remains deferred under the current sprint convention.

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