chore(core): dead-code audit — remove zero-consumer modules

[KealanAU]

Repo-wide dead-code audit: everything removed here was verified to have zero consumers at the symbol level across core, kit, cli, tools, and all example apps (barrel re-exports and own tests excluded).

• Remove the unexported shared/color/ module (~1,900 lines) — ported for ColorArea/ColorSlider primitives that were never built
• Remove all 31 *.story.vue files (~3,200 lines) — no story runner exists in the repo; story/_*.vue test fixtures are untouched
• Remove the hand-maintained constants.ts export registry (components/originals/utilities) — no consumer in tools, docs, or tests
• Remove unused lynx-ui-common ports: selector.ts, version.ts, getEventDetail, mainThreadify, popoverUtils, convertToPx (+ tests)
• Remove unused reka-ui ports: useKbd, useGraceArea, useSelectionBehavior, useFormControl, isValidVNodeElement, withDefault, useScrollTo, Arrow.vue, countryList (+ tests)
• Drop vue-component-type-helpers from runtime deps — sole importer was withDefault, and type-only at that
• useId: drop the Vue <3.5 fallback branch (all workspaces pin 3.5+); fix stale docblocks in dragGesture.ts/scan-dts.ts that referenced removed or never-built modules

Deliberately kept despite zero internal callers: useStateMachine, useLocale, useDateFormatter — each has a dedicated docs page and is intentional public API (i18n is documented as partially built). Removing those is a product call for a separate PR.

Note: withDefault, useScrollTo, and the constants.ts registry were public exports, so this is technically API-breaking — flagged in the changeset per AGENTS.md, kept at patch per pre-1.0 policy.

Net: −8,219 lines, −1 dep. Core + kit typecheck/test/build pass, cli tests pass, kit-demo builds cleanly.