update/refact - #38

…g fixes and audits

- layouts: xtop-layout crate (repo layouts) with user-wins overrides; xtop layout check/install
- widgets: packs via xtop-widget-api; engine resolves (pack, name); base pack + blocks alt
- functioning: rates, chart, PID-anchored kill, per-tick snapshot cache, event loop (ctrl+c/paste/mouse), config merge, theme overrides, versioned asset seeding
- plugins split into list/install/scaffold; help from live keybindings; audit script; app.rs split

- delete dead plugins_dir_tmp; AlertThresholds from plugin-api (byte-identical config JSON); PluginWidget import replaces PluginWidgetFn
- providers drop docker surface; unknown layout widget ids warn once
- themes: miami embedded+seeded, runtime count corrected to 12; themes_dir via platform-aware config_dir
- ratatui 0.30.2 + single crossterm 0.29; rust-version 1.87
- effects feature (off by default) wiring xtop-effect-fade into the draw path
- version 0.3.0; CHANGELOG, README, docs/ (incl. moved colors.md), install scripts, kernel ROADMAP and audit.sh synced to reality
- drop kernel-local to_color (import canonical widget-api glyph helper)