Revert "feat(knowledgebase): replace litellm-pgvector connector with memory-retrieval"

This reverts commit abeadc49c8.

Restores vendor/litellm-pgvector/ and the vector_store_registry wiring
(in-band file_search tool-call support) at the user's request, after
re-confirming against docs.litellm.ai/docs/completion/knowledgebase and
litellm-pgvector's own README that pg_vector is still not an in-process
vector_store_registry backend -- it requires this same standalone
connector service either way, so there is no simpler 'native' path that
was missed. Trading back in: 793 lines of vendored code, the untested
Prisma migration, and the git-context build risk noted in VENDORED.md
(all flagged as unverified against real hardware in issue #24), in
exchange for the file_search in-band tool call memory-retrieval did not
support.

Conflicts resolved on top of later commits (Redis, update.sh key-minting
fold-in):
- .env.example / docs/memory-knowledgebase.md: kept the auto-mint-via-
  update.sh language, renamed MEMORY_RETRIEVAL_* back to
  LITELLM_PGVECTOR_*.
- scripts/generate-secrets.sh: left deleted -- its job was folded into
  update.sh in 24d749b, unrelated to this revert.
- scripts/update.sh: renamed the MEMORY_RETRIEVAL_* secret/mint calls to
  LITELLM_PGVECTOR_* to match.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018WHfjWrSEcGhCoeu6dQfDa

scripts/update.sh

@@ -39,7 +39,7 @@ set_if_blank LITELLM_DB_PASSWORD "$(openssl rand -hex 32)"
 set_if_blank REDIS_PASSWORD "$(openssl rand -hex 32)"
 set_if_blank UI_PASSWORD "$(openssl rand -hex 16)"
 set_if_blank PGVECTOR_DB_PASSWORD "$(openssl rand -hex 32)"
-set_if_blank MEMORY_RETRIEVAL_API_KEY "$(openssl rand -hex 32)"
+set_if_blank LITELLM_PGVECTOR_API_KEY "$(openssl rand -hex 32)"
 
 echo "==> resolving SEARXNG_LAN_IP"
 # search.home is a LAN mDNS/local-DNS name — resolvable from this host, just
@@ -66,7 +66,7 @@ docker compose build --pull
 echo "==> bringing up litellm (needed to mint virtual keys below)"
 docker compose up -d --wait litellm-db litellm
 
-# OPENWEBUI_LITELLM_KEY / MEMORY_RETRIEVAL_EMBEDDING_KEY are per-workload
+# OPENWEBUI_LITELLM_KEY / LITELLM_PGVECTOR_EMBEDDING_KEY are per-workload
 # virtual keys, not random secrets — minted via LiteLLM's own API
 # (docs/proxy-key-onboarding.md documents the manual Admin UI route; this is
 # the same thing over the REST endpoint LITELLM_MASTER_KEY already
@@ -96,7 +96,7 @@ mint_key_if_blank() {
   fi
 }
 mint_key_if_blank OPENWEBUI_LITELLM_KEY openwebui
-mint_key_if_blank MEMORY_RETRIEVAL_EMBEDDING_KEY memory-retrieval
+mint_key_if_blank LITELLM_PGVECTOR_EMBEDDING_KEY litellm-pgvector
 set -a && . ./.env && set +a
 
 echo "==> recreating changed services"