fix: Remove a test chunk that leaked into the shipped RAG index

A local smoke test for the /api/upload ingestion path (add_chunks + save)
wrote its test fixture straight into data/rag_index/chunks.json, which then
got shipped in the previous commit. Removed it and rebuilt the index.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

data/rag_index/bm25.pkl

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:a44f807feb5042e172378e8a08783266ea1a6aa5788fc37aa5adb28bf2fc20db
-size 9492608
+oid sha256:aec368fab52a30b88e2bc1633add98c1f6a0a8f5260ad50d73d965381c741210
+size 9492413

data/rag_index/chunks.json

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:2b744f1fb462b3cfc345f24411853b88b6b23fda26459632990a8fc4d3b24841
-size 12949232
+oid sha256:939cfc3169818185b3dd60ba12b2e4799fd10755fd0fcbbff8f390567761c091
+size 12948944