Adopt the loc runtime end to end; retire the Crowdin pipeline

Moves all on-device text through the ui-core localization runtime, converts
the legacy translations into source-string-keyed catalogs maintained in-repo,
and replaces the Crowdin build scripts with a per-language build
generator. English builds are behavior-identical (fonts resolve to the same
bitmaps.font8 object; strings resolve to their source values).

What changed

Runtime adoption

• tooltips.ts rewritten as a derived file: an id -> source-string map
  (tooltipTable) plus tooltip(id), with resolveTooltip(id) now
  returning ui.loc(tooltip(id)). tooltip2tid preserved for the web-only
  tooling. Regenerated from locales/tooltips.json by
  scripts/tooltipgen.mjs (single source of truth; regeneration is
  byte-stable). The orphaned lang/font constants are removed.
• Fonts: control styles no longer bake font: bitmaps.font8 (the ui-controls
  render fallback resolves locFont() at use time); direct draw/measure
  sites call ui.locFont(). The ControlPicker title now passes an explicit
  font, closing the last draw of localized text that relied on font
  auto-selection. The home-screen tagline and version deliberately stay in
  font5.
• Raw literals wrapped at use sites ("OK", the settings-screen strings).
  The missing "delete" tooltip key is added, and the tile-suggestion delete
  button's style now composes FocusLabel, so its label renders on focus
  like its grid siblings instead of inline.
• loc.g.ts (new, first in the pxt.json files list): the per-language
  translation table slot. The committed default assigns nothing; its header
  documents why the file exists, the load-order constraint, and that
  non-default states are transient build intermediates.

Catalogs

• locales/tooltips.json is the id-keyed master; locales/<lang>.json are
  source-string-keyed translation catalogs for 23 languages, converted from
  the legacy assets/strings data and then filled to ~97% coverage (the
  remaining gaps are dead-tile placeholders and a short low-confidence list
  documented for native review). Missing keys fall back to the source string
  at runtime, so partial catalogs are always safe.
• locales/README.md documents the catalog rules, the add-a-string workflow,
  coverage checking, and the constraints that preclude CJK support on this
  platform (font, flash, rendering); the four CJK catalogs are kept as data.

Tooling

• scripts/locgen.mjs: merges the ui-core, ui-controls, and app catalogs
  (app wins), drops identity entries, validates every translation against
  font8's actual glyph table (tagline against font5, since it renders in the
  small font), emits loc.g.ts, and builds
  assets/hex/microcode-v2.<lang>.hex per language. Languages with no
  renderable translations are skipped. --coverage [--verbose] reports
  per-language translation coverage without building.
• scripts/locstrings.mjs and scripts/tooltipgen.mjs regenerate the
  derived files; npm run loc:strings|loc:tooltips|loc:regen|loc:coverage|loc:hex|loc:verify.
• Crowdin pipeline removed: scripts/lochex.mjs, the one-time catalog
  converter, and the node-fetch dependency are gone. The deployed web
  page's runtime strings (assets/strings/<lang>/tooltips.json) are now
  generated by locgen on every run from the catalogs, so the web surface
  tracks the same source of truth as the device builds -- including CJK
  languages, which localize on the web (browser fonts) even though they
  build no hex. Sample-name (N*) translations live in the catalogs and
  ship web-only, never occupying device flash.
• .github/copilot-instructions.md updated to point contributors at the
  catalogs and ui.loc(...).

Verification

• English build verified pixel-identical: per-site font audit (every path
  resolves the same bitmaps.font8 object as before) and simulator pass.
• All 20 buildable language images build green with zero glyph drops; the
  four CJK languages skip themselves (no renderable translations).
• Hardware-verified on device: fr, pl, and es-ES images, including accented
  glyph rendering.
• Flash cost measured: English image unchanged; a Latin-language image adds
  roughly 1-3KB of table data. Remaining image headroom measured at ~29KB.
• Web snapshots regenerated for all 24 languages and spot-checked against
  the legacy files; device tables and hex sizes verified unchanged by the
  web-surface work.

Release note

Parked as draft until ui-controls bump, pending microbit-apps/ui-controls#1