Query values such as ?id=a=b=c were truncated to a, because parseQuery split at every equals sign and kept only the second part. Split out the entire remainder after the first equals sign so route queries preserve their values.

Fixes #2810.

Regression coverage includes multiple/lone equals signs, percent-encoded equals signs, plus-to-space decoding, empty values and valueless parameters.

Validation:

• Confirmed the new regression fails on the original code and passes with the fix.
• npm run test:jest -- --runInBand: 13 suites, 129 tests, 46 snapshots passed.
• npm run typecheck: passed.
• npm run build: passed.
• Prettier and ESLint checks for changed files, plus git diff --check: passed.

Assisted by Codex; reviewed the complete diff and ran these checks locally. The full Playwright browser matrix was not run locally.