refactor: update environment configuration, enhance installation script, and add migration scripts for database setup

docs/database/0006-pgvector-and-embeddings.md

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+# 0006 - pgvector And Embeddings
+
+SQL file: `supabase/migrations/0006_add_pgvector_and_embeddings.sql`
+
+## Purpose
+
+Adds vector storage for future retrieval augmented generation features.
+
+## What It Creates
+
+- `vector` extension
+- `document_embeddings`
+- `match_documents()`
+
+## RLS
+
+Embeddings are scoped by `user_id`; users can manage only their own embedding rows.
+
+## Notes
+
+The migration expects the target Postgres/Supabase environment to support the `vector` extension.
+
+## Execution
+
+Run after `0005_add_advanced_crm_tables.sql`.