Add targeted comments explaining non-obvious behaviour

- embedder.py: lazy model load rationale, RGB conversion, shared vector space
- main.py: why vec appears twice, ::vector cast, 1-distance score formula
- main_oracle.py: why array.array("f") is required instead of plain list
- main_oracle_indb.py: no embedder import — embedding done inside Oracle SQL
- index_images_oracle.py: same array.array requirement on indexing path

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

oravector-demo/backend/main_oracle_indb.py

@@ -1,3 +1,5 @@
+# No embedder import — text embedding happens inside Oracle via VECTOR_EMBEDDING(CLIP_TXT).
+# The only value Python passes to the database is the raw query string (:q).
 import os
 from fastapi import FastAPI, Query
 from fastapi.middleware.cors import CORSMiddleware