Normalize count-mode output format validation

[Widthdom]

Summary

• Normalize --count and --format count before output compatibility validation.
• Preserve the rightmost explicit format while rejecting incompatible row formats, JSON stream/projection modes, and compact bounded responses instead of silently overriding count output.
• Keep count output script-compatible across numeric, JSON object, array, and envelope shapes, including audit's structured JSON usage errors.

Validation

• Full Release net8.0: 10,841 passed, 7 skipped, 0 failed.
• Full Release net9.0: 10,367 passed, 420 skipped, 0 failed.
• After the final origin/main sync:
  • Release solution build: 0 warnings, 0 errors.
  • ProgramRunnerTests: 333/333 passed on both net8.0 and net9.0.
  • Newly merged Issue Reject incompatible FTS and literal search modes #4879/Add a byte budget to outline JSON #4880 integration tests: 5/5 passed on both targets.
• Changelog fragment validation: 55 fragments validated.
• Repository index: final HEAD is fresh, matches the workspace, and has no failed readiness checks.
• git diff --check origin/main...HEAD.

Documentation and changelog

• Updated the English and Japanese count-mode contracts in USER_GUIDE.md and TESTING_GUIDE.md.
• Added changelog.d/unreleased/4878.fixed.md.

Adversarial review

• Round 1 identified the --results-only count-schema conflict; the conflict is now rejected with regression coverage.
• Round 2 identified explicit count format loss through later modifiers and audit's structured JSON error bypass; both findings are fixed with regression coverage.
• All actionable findings from the two workflow review rounds were addressed and revalidated.

Follow-up

• Do not consume json-envelope when it is an option value #4976

Fixes #4878