The JSON/YAML tree viewer (#484) hardcoded its default: valid json/yaml
fenced blocks opened in Tree view at 10+ lines (`const showTree=lineCount>=10;`).
Make that default user-configurable while preserving current behavior.
- New settings (persisted via /api/settings -> settings.json):
- structured_code_default_view: auto | on | off (default auto)
- structured_code_auto_tree_lines: int 1..1000 (default 10)
- ui.js: replace the hardcode with a sanitized, unit-testable decision
helper _structuredCodeShowTree(mode, threshold, lineCount); Tree/Raw
toggle, Raw <pre><code>, parse-failure fallback, and YAML lazy-load
are unchanged.
- Appearance settings: 'JSON/YAML code blocks' select + 'Auto threshold
lines' input (disabled outside auto mode); wired through the existing
appearance-autosave and explicit-save paths; live re-render on change.
- boot.js seeds window globals; i18n labels added to all 13 locales.
- Default (auto + 10) reproduces the original >=10 behavior exactly.