fix(pregate): resolve extensionless .jsx, .mts, .cts and index.jsx/tsx/mjs imports (#3340)

RESOLVE_EXT had no .jsx and no index.jsx/index.tsx/index.mjs, so on a JSX repo
every extensionless component import resolved nowhere and lanes failed with
'has no test lane'. Existing entries keep their order (it decides precedence).

Fixes #3340

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

docs/pregate.md

@@ -137,6 +137,10 @@ Two stages with separate clocks, both printed:
   included, are source code, so a `dependencies` `[]` declaration clears them and `empty_lanes`
   does not), transitively through
   non-test files; deleted and renamed files select the tests that named them.
+  An extensionless JS/TS import (relative, a tsconfig/jsconfig `paths` alias or
+  `baseUrl`) tries the exact path, then `.ts`, `.tsx`, `.js`, `.jsx`, `.mjs`,
+  `.cjs`, `.mts`, `.cts`, then `index.ts`, `index.tsx`, `index.js`, `index.jsx`
+  and `index.mjs` inside the directory; the first file that exists wins.
   A touched source file with no lane is `FAIL lanes — <file> has no test lane`,
   never a pass. Markdown that no test depends on is a docs/no-tests empty lane
   instead (`docs/no-tests: N documentation file(s)`), including when the base