jnv jee_results: 2025 NTA export missing name/DOB + all board-marks fields (2023/24 missing year_of_passing_12)

The raw NTA JEE-Mains exports staged in `gs://avantifellows-external-data/jnv/raw/jee_mains/`
are inconsistent across years — several demographic/board blocks are **absent from the
source files themselves** (not a transform bug):

- **2025** (`jee_2025_-_all_jnv_candidates.parquet`, 12,103 rows): no `student_full_name`,
no `dob`, and **no 10th/12th board fields at all**. It does carry `avanti_studentid`
(now retained after the codemap fix), so roster linkage is fine — but grade-10/12 marks
cannot come from NTA for 2025; they must be sourced from
`jnv_fact_board_results_10th` (exam_year 2023) or `dim_student` self-report.
- **2023 + 2024**: `year_of_passing_12` is blank (unlike 2021/2022/2025/2026).
- **2026**: complete (name, dob, year_of_passing_10/12, inline 10th marks).

### Ask
Re-pull the **2025** (and ideally 2023/2024) NTA exports with the full demographic + board
block as provided for 2024/2026, so name/DOB and grade-10/12 marks are available uniformly
across years.

### Context
Surfaced while linking JEE outcomes to grade-10 board marks for the centre cohorts.
Paired with the codemap fix PR (recovers 2024 10th/12th + carries the Avanti student id).

Start with the raw exports in gs://avantifellows-external-data/jnv/raw/jee_mains/, especially jee_2025_-_all_jnv_candidates.parquet, and compare their demographic and board columns with the 2024 and 2026 exports. Re-pull the requested 2025 data and, if possible, 2023/2024; done means the expected name, DOB, passing-year, and board-mark fields are available consistently, with avanti_studentid retained.

Written by the indexing model from the issue text.