feat: support empty-array default in string syntax ( = [])

[SynthLuvr]

Resolves #1169

Summary

Allow defaulting a property to an empty array using the concise string
syntax, e.g. type({ values: "string[] = []" }), instead of resorting to
the verbose tuple-with-initializer workaround.

Motivation

Quoting #1169 — in ~90% of cases where a property needs a default, the
default is an empty array, yet today you must write a lot of boilerplate:

scope({
  item: { foo: "string" },
  currently: ["item[]", "=", () => []],
  suggested: "item[] = []",
})

Implementation

• parser/shift/operator/default.ts — runtime parseDefault
  short-circuits an [] token to a fresh-array thunk () => [], so each
  traversal that falls back to the default gets a brand-new array (matching
  the existing tuple workaround). Type-level parseDefault accepts []
  and exports a new inferDefaultLiteral alias.
• parser/ast/infer.ts — inferExpression uses inferDefaultLiteral
  so an [] default infers as never[].
• parser/ast/default.ts — validateDefault accepts [], verifying
  the base type is array-like (never[] assignable to the input type).

The bundled docs/components/dts/type.ts preview that was incidentally
regenerated during development has been reverted so it is not part of this
change.

Checklist

• Tests added (ark/type/__tests__/arrays/defaults.test.ts,
  ark/type/__tests__/objects/defaults.test.ts)
• type({ values: "string[] = []" }) works
• Each traversal gets a fresh array

[pullfrog]

ℹ️ No critical issues — minor suggestions inline.

Reviewed changes — adds support for empty-array defaults in string syntax ("string[] = []") with runtime fresh-array thunks and type-level validation.

• Runtime parser in parser/shift/operator/default.ts short-circuits [] to () => [] so each traversal gets a fresh array.
• Type-level parser in parser/ast/default.ts accepts [] as a default literal when the base type is array-like.
• Type inference in parser/ast/infer.ts maps the [] literal to never[].
• Tests in __tests__/arrays/defaults.test.ts and __tests__/objects/defaults.test.ts cover tuple literals, fresh references, equivalence to tuple thunks, trailing-junk rejection, and non-array base rejection.

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