chore: gitignore preprint build products (packages/, .build/, PACSeries.zip)

Part of the Press rebuild (bert ADR-0029). Removes ~170MB of package
artifacts from the index (working tree untouched, no history rewrite).
Reproducibility moves to the RELEASES.yaml ledger: git_commit + source_hash
+ package sha256 per release; canonical copies live on Zenodo.

Author: lornecodes

.changelog/20260705_161500_press-package-hygiene.md

@@ -0,0 +1,15 @@
+# Package hygiene: stop tracking preprint build products
+
+Part of the Press rebuild (bert ADR-0029). `foundational/docs/preprints/packages/`
+(~170MB of timestamped package dirs + zips), `preprints/.build/`, and the root
+`PACSeries.zip` are now gitignored and removed from the index (working tree
+untouched — files remain on disk; no history rewrite, so DOI'd artifacts stay
+reachable at old commits).
+
+Reproducibility is preserved a better way: the forthcoming
+`preprints/RELEASES.yaml` ledger records git_commit + source_hash + package
+sha256 per release, so any published zip is rebuildable from source at the
+recorded commit — and the canonical copy lives on Zenodo.
+
+`packages/UPLOAD_CHECKLIST.md` (the old manual upload checklist) goes untracked
+with the rest; it is superseded by the press validation suite + ledger.

.gitignore

@@ -146,3 +146,9 @@ cimm.log
 
 # Session research notes
 SESSION_NOTES.md
+
+# Press build products (ADR-0029, bert): packages are rebuildable from source at the
+# commit recorded in preprints/RELEASES.yaml; canonical copies live on Zenodo.
+foundational/docs/preprints/packages/
+foundational/docs/preprints/.build/
+foundational/docs/preprints/PACSeries.zip