Add two Visa new grad OA practice questions

[tomtoto757]

Two published Visa coding exercises are missing from the question bank. This adds their canonical FastPrep titles and practice links, with the latest reported date of Aug 31, 2026:

• Collect Branches for a Bird Nest
• Count Reverse-Digit Pairs

The public metadata identifies both as Visa new-grad OA problems. The README and Coding page now contain 2,141 and 1,809 rows respectively. All 2,139 prior README rows, 1,807 prior Coding rows, their relative order, and the company list are unchanged.

README.md remains the authored source. The generated formats/coding.md change is required by the current CONTRIBUTING.md workflow and keeps the linked Coding page consistent. This PR changes only those two Markdown files; it includes no problem statements, solutions, source images, runtime code, or workflow changes.

Verification:

• python3 scripts/refresh-freshness.py passes and is idempotent: zero marker changes and zero reordered positions on the final run.
• python3 scripts/sync-practice-formats.py and python3 scripts/sync-practice-formats.py --check pass against the current public catalogs.
• PYTHONDONTWRITEBYTECODE=1 python3 -m unittest scripts/test_sync_practice_formats.py passes all 11 tests.
• Complete table verification passes for paired canonical URLs, unique company/route keys, descending dates, stable ties, exact generated Coding-page content, and preservation of all prior rows. Both production APIs and canonical pages return HTTP 200 with matching metadata and titles.
• git diff --check origin/master...HEAD passes.

An independent Codex reviewer, source_review, reviewed final head af8001ae1005ce26c9b9f7b82d749842ed196d21 against current master f3e590c5989831ef597def6d1d8797c34d717b38. The review covered the complete diff, native contribution contract, generator and hourly consumer, all-row invariants, published metadata, canonical routes, and publication eligibility. The reviewer independently reran the native check, all 11 tests, full table verification, public HTTP checks, freshness idempotence, and whitespace validation. No findings remain.

The native checker still reports 158 pre-existing legacy routes absent from the public catalog; none is introduced by this change. README is 495,300 bytes, below the native 500,000-byte limit. Application type checking and builds are not applicable to this Markdown-only change. This is a draft PR; no merge or deployment is requested.