Add size-first encode defaults

[shiny-code-bot]

Summary

• add DB/runtime-backed encode defaults for a size-first review model: 300 MB per 45-minute episode, max 1080p, VMAF floor 80, and current ab-av1 fast sample engine
• expose those defaults on Settings and send them into the folder tuning runtime toolbelt so assistant proposals treat size as the primary goal and metrics as guardrails
• harden /review-media static serving for web smoke review routes and remove dead folder-studio helper exports found during inspection

Validation

• bash scripts/pre-commit-check.sh
• Browser QA on http://127.0.0.1:8777/settings: encode defaults render with 300 MB / 45 min, max 1080p, and no horizontal overflow at the checked viewport
• PyCharm changed-files closeout ran; remaining findings are pre-existing weak shadowing warnings in the broad backend recovery test file

Refs #101
Refs #102