fix(litellm-pgvector): vendor the source instead of a remote git build context

The server's Docker/BuildKit couldn't do a git-context build of a public
github.com repo (fails with "could not read Username ... terminal prompts
disabled" — an auth-shaped error for what should be an anonymous clone).
Rather than debug that, vendor litellm-pgvector's small source tree
directly (vendor/litellm-pgvector/, see VENDORED.md for provenance/update
steps) and build from the local path.

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

docker-compose.yml

@@ -216,14 +216,19 @@ services:
   # LiteLLM's native knowledgebase/vector-store feature has no Qdrant backend
   # (the qdrant service above only serves Open WebUI's own RAG/Memory) — this
   # companion service (github.com/BerriAI/litellm-pgvector) is the only
-  # self-hosted path. No published image exists yet, so this builds straight
-  # from the upstream repo. See docs/research/litellm-knowledgebase.md.
+  # self-hosted path. No published image exists yet, so this builds from a
+  # vendored copy in vendor/litellm-pgvector/ (see that dir's README) rather
+  # than a remote git build context — the server's Docker/BuildKit couldn't
+  # do an authenticated-looking clone of a public github.com repo (fails
+  # with "could not read Username ... terminal prompts disabled"), and
+  # vendoring sidesteps needing that debugged. See
+  # docs/research/litellm-knowledgebase.md.
   # ponytail: unverified against real hardware — Prisma migration behavior on
   # first boot and the exact vector_store_registry field names for the
   # pg_vector provider need a live smoke test. See issue #24.
   litellm-pgvector:
     build:
-      context: https://github.com/BerriAI/litellm-pgvector.git
+      context: ./vendor/litellm-pgvector
     container_name: litellm-pgvector
     depends_on:
       pgvector-db: