fix(tooling): a template-literal mode for the vocabulary gate's four shared textual scanners (#14626) (#14739)

`scanTopLevel`, `enclosingOpeners`, `sliceBalanced` and `splitTopLevel` each
carried the same seek-to-matching-quote skip, which a NESTED template literal
walks straight out of: the outer template closed at the first inner backtick
and every `code:` position after it in that file went unplaced.

All four now call ONE shared `skipStringLiteral`, a small state machine that
tracks `${ … }` nesting and recurses into literals opened inside an
interpolation. `enclosingOpeners` answers every requested index with a TAGGED
result, so "genuinely inside a string" and "the scanner lost its place" stop
arriving as the same `undefined`; the other three take an optional
`scanReport()`. The tag is certified — `inside-string` is asserted only for a
walk that ends with no unterminated literal, no bracket underflow and an empty
stack.

`--self-test` gains a nested-template fixture per primitive, each PAIRED with a
positive control run through the pre-fix `legacySeekQuote` kept in test scope.

`OBJECT_LITERAL_CODE_HELPER_BLINDNESS` and `INLINE_LITERAL_EXPRESSION_CENSUS`
are re-derived on this tree, with tree drift separated from what the fix moved,
and `SCANNER_LITERAL_BLIND_SPOTS` records the residual class the sweep found
(a regex literal carrying a quote) rather than leaving it to be rediscovered.


Claude-Session: https://claude.ai/code/session_01WLJQhde67SeTccsmnBVarV

Co-authored-by: Claude <noreply@anthropic.com>

Author: claude[bot]