v0.2.0 - drop Cascadia, real iPad layout fix, dev debug overlay

Changed

• --mono-stack falls through to ui-monospace / SFMono-Regular
  instead of pulling in Cascadia Code. The font-display: optional
  swap that drove the iPad Safari layout shift (fresh visit computed
  against the fallback, second visit against the cached webfont) no
  longer exists because there is no webfont.
• Real grid fix for the "main column shifts right on long code lines
  or wide TOC titles" iPad bug:
  grid-template-columns: var(--col-aside) minmax(0, 1fr),
  .main { overflow-x: hidden }, pre/.highlight { min-width: 0 }.
  Together these stop descendant min-content from inflating the main
  track.
• Inline <code> drops the bottom border (previously read as a link)
  and gains muted backtick pseudo-elements. Matches the terminal
  voice and mirrors the Markdown source.

Added

• Dev-only debug overlay at layouts/_partials/debug.html. Renders
  two pills when hugo.IsServer or CF_PAGES_BRANCH != "main":
  a viewport / page-box / sidebar-box / main-box / computed grid
  template readout with tap-to-copy JSON, and an auto-reload toggle
  that polls the current URL every 5 s and reloads only when the
  modeline SHA changes. Scripts live in assets/js/overlay.js and
  assets/js/autoreload.js, minified and fingerprinted via
  js.Build. Production on main ships zero bytes of this.
• jsconfig.json enables strict checkJs across assets/js/**.
• .github/workflows/ci.yml builds exampleSite/ on every PR as a
  lightweight sanity gate; actions/checkout pinned to v5.0.1 by SHA.
• exampleSite/hugo.toml allowlists CF_PAGES_* and COMMIT_SHA in
  security.funcs.getenv so the modeline footer's os.Getenv call
  clears Hugo's default policy on consumer sites.

Removed

• static/fonts/cascadia/*.woff2 (normal + italic variable faces),
  assets/scss/_fonts.scss, and the @import "fonts" in
  rest.scss. No more web fonts shipped.