Extract testable type core, add JS tests, decompose hot spots

Extract testable type core, add JS tests, decompose hot spots

Tests for the unification/matching core (review item #1):
  - Move the pure TypeArg unification/matching functions out of viewer.js
    into data/typecore.js, a DOM-free module exposing the data-free helpers
    directly and the data-dependent ones (reduceTypeArg, substTypeArg,
    findMatchingInstances) via makeTypeCore(env). viewer.js binds them to the
    program's family index + instance list and destructures the names it uses.
  - data/typecore.js is embedded into the page (Render.hs + viewer.html) as a
    <script> before viewer.js, and required directly by the Node test-suite.
  - test/typecore.test.js: 19 fixtures covering one-sided instance matching
    incl. multi-param projection, closed/open family reduction, and the
    data-family / chain rewrite (replaceFamilyApp).
  - test/views.test.js + test/harness.js: a stub DOM/Cytoscape harness loads
    viewer.js headlessly and exercises buildInstanceView (satisfied vs
    external superclass edges). test/snapshot-views.js dumps every builder's
    output for before/after refactor diffs.
  - package.json: `npm test` → `node --test test/*.test.js` (22 tests, no deps).

Decomposition (review item #2):
  - Extract.hs: split typeArg into typeArg / tyConArg / dataFamilyRepArg.
    Verified behaviour-preserving — demo dumps are byte-identical.
  - viewer.js: lift the three per-instance phases (context, associated
    families, superclass requirements) out of buildInstanceView's row loop
    into named inner helpers. Verified byte-identical view output across all
    23 demo views via the snapshot harness.

Warning (review item #3):
  - Render.hs: rename the `head` binding in familyNodeLabel that shadowed
    Prelude.head (clears the -Wname-shadowing warning).

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>