Add ADVENT (NEJMoa2307291 / NCT04612244) — missing from source corpus

## What

Adds the ADVENT trial, absent from the corpus until now:

- `documents/10.1056_nejmoa2307291/` — protocol + SAP, each with the full format set
(`.pdf`, `_mmd.zip`, `_tex.zip`, `.html`, `.lines.json`)
- `data/tdr.parquet` — row 1642

## Why it was missing

Not a download failure and not a paywall. The corpus reconciles exactly
(1641 rows <-> 1641 folders, zero `*.error.txt`), so the pipeline was healthy —
the row was simply never entered in the curation sheet, and `sync_dataset.py` is
sheet-driven and additive, so a trial nobody types in produces no row, no
folder, and no error.

The protocol and SAP were both posted on ClinicalTrials.gov the whole time, at
the exact URL pattern the pipeline already uses.

## Notes for review

- **Protocol revision.** `Prot_002.pdf`, taken from the API's
`largeDocumentModule.largeDocs[].filename`. `Prot_000.pdf` also returns HTTP
200 but is a superseded revision — the CDN keeps serving old ones. Worth a
broader audit: 1735 existing links use the `_000` suffix.
- **`Trial Design: adaptive_bayesian;noninferiority`.** From the SAP: Bayesian
primary analysis with non-informative priors, Goldilocks adaptive sample
sizing (350-750), non-inferiority margins 0.08 (safety) / 0.15
(effectiveness); superiority is a secondary endpoint only. Existing
vocabulary value, used by 6 other rows.
- **`Lead Sponsor: Boston Scientific Corporation`** per ClinicalTrials.gov. The
protocol says `FARAPULSE, Inc.` (acquired mid-trial); CT.gov was kept for
consistency with the other 1641 rows.
- **`Statistician*` left null.** The posted SAP is unsigned (`Author: ____`) and
the protocol names no statistician. 1204/1641 existing rows are null here.
- **Schema change:** the all-null `Unnamed: 22` / `Unnamed: 23` columns are
dropped (24 -> 22). They were artifacts of trailing sheet columns. This
rewrites every row group, so the parquet shows as a full-file change rather
than a one-row append — no other row content is modified.

The same row still needs adding to the curation sheet, otherwise the next full
`sync_dataset.py` run regenerates the parquet from the sheet and drops it.

.gitattributes

@@ -5769,3 +5769,5 @@ documents/10.1200_jco.21.02678/protocol.html filter=lfs diff=lfs merge=lfs -text
 documents/10.1056_nejmoa2105215/protocol.lines.json filter=lfs diff=lfs merge=lfs -text
 documents/10.1056_nejmoa1812792/protocol.lines.json filter=lfs diff=lfs merge=lfs -text
 documents/10.1056_nejmoa1812792/sap.lines.json filter=lfs diff=lfs merge=lfs -text
+documents/10.1056_nejmoa2307291/protocol.pdf filter=lfs diff=lfs merge=lfs -text
+documents/10.1056_nejmoa2307291/sap.pdf filter=lfs diff=lfs merge=lfs -text

data/tdr.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:7adb59120298d18f58fbd5006e47302551d487ad5b76c8f47eb6b6478e243169
-size 707253
+oid sha256:3535a94b2487d7eead6b610103008a0aa8a0b2d6609a877d64764f4a750cb643
+size 716967

documents/10.1056_nejmoa2307291/protocol.pdf

@@ -0,0 +1,3 @@
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+size 2018849

documents/10.1056_nejmoa2307291/protocol_mmd.zip

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+size 1120981

documents/10.1056_nejmoa2307291/protocol_tex.zip

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+size 1133309

documents/10.1056_nejmoa2307291/sap.pdf

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+size 1086006

documents/10.1056_nejmoa2307291/sap_mmd.zip

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documents/10.1056_nejmoa2307291/sap_tex.zip

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