fix(migrate): ctx codemod no longer rewrites inside strings and comments

[JonasJesus42]

Context

The transformCtxCompat codemod (Fresh → TanStack migration) turns ctx reads into optional chains, so that
an app not configured on the target site yields undefined instead of throwing — without it,
withSectionLoader swallows the exception and the section renders blank.

It walks the file character by character, with no notion of string or comment boundaries. The result is
that a ctx. appearing as text was rewritten just like one appearing as code:

console.log('ctx.device:', ctx.device);
// becomes
console.log('ctx?.device:', ctx?.device);

The call site is patched correctly and the message next to it is silently corrupted. And it compiles, so
nothing catches it — not the build, not typecheck, not tests. Same for double-quoted strings, line and block
comments, and template literal text.

No test covered this.

What changes

A literal/comment guard in the scan loop. On //, /* */, '…' or "…", the span is copied verbatim
instead of scanned.

Template literals are not skipped wholesale, because their interpolations are real code. They are tracked
with a small context stack, so:

`${ctx.vtex.account}`   →   `${ctx?.vtex?.account}`   // code: rewritten
`ctx.device`            →   `ctx.device`              // text: preserved

This also covers nested templates (`a${`b${ctx.device}`}c`) and escaped quotes inside strings.

Regex literals are deliberately left out, and the reason is in a code comment: telling /re/ from a
division requires real parsing, and guessing wrong would make the scanner consume live code. A ctx. inside a
regex in a loader is vanishingly rare next to that risk.

Why not ts-morph

blocks-cli already depends on ts-morph, and rewriting via AST would eliminate the entire bug class rather
than the cases we happened to think of. I didn't do it here because the scanner carries subtle, already-tested
logic (isAssignTarget, already-optional chains, balanced computed access), and the rewrite would carry
regression risk out of proportion to the bug. Noting it as a known path if the scanner needs to grow again.

Validation

Five regression tests. Four of them fail against the previous implementation — verified by reverting the
source and re-running, so the tests aren't decorative:

× does not rewrite ctx inside string literals
× does not rewrite ctx inside double-quoted strings or escaped quotes
× does not rewrite ctx inside comments
× does not rewrite template text but DOES rewrite ${} interpolation

13 tests in the file (8 existing + 5 new), all passing. Full suite at 2589 passing; the 4 draft preview
failures are pre-existing on main. Lint and typecheck clean.

Provenance

Found by a /code-review that announced itself as being for #510. It isn't: #510 had 16 files and none of
them was ctx-compat.ts (checked via the GitHub API). The review most likely ran against another workspace's
local diff. The bug is real and independent of any PR, hence this going separately.

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