Simplify SQLMesh to use single prod gateway with virtual environments

- Remove dev gateway (local DuckDB file no longer needed)
- Single prod gateway connects to R2 Iceberg catalog
- Use virtual environments for dev isolation (e.g., dev_<username>)
- Update CLAUDE.md with new workflow and environment strategy
- Create comprehensive transform/sqlmesh_materia/README.md

Benefits:
- Simpler configuration (one gateway instead of two)
- All environments use same R2 Iceberg catalog
- SQLMesh handles environment isolation automatically
- No need to maintain local 13GB materia_dev.db file
- before_all hooks only run for prod gateway (no conditional logic needed)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

transform/sqlmesh_materia/README.md

@@ -0,0 +1,92 @@
+# Materia SQLMesh Transform Layer
+
+Data transformation pipeline using SQLMesh and DuckDB, implementing a 4-layer architecture.
+
+## Quick Start
+
+```bash
+cd transform/sqlmesh_materia
+
+# Local development (virtual environment)
+sqlmesh plan dev_<username>
+
+# Production
+sqlmesh plan prod
+
+# Run tests
+sqlmesh test
+
+# Format SQL
+sqlmesh format
+```
+
+## Architecture
+
+### Gateway Configuration
+
+**Single Gateway:** All environments connect to Cloudflare R2 Data Catalog (Apache Iceberg)
+- **Production:** `sqlmesh plan prod`
+- **Development:** `sqlmesh plan dev_<username>` (isolated virtual environment)
+
+SQLMesh manages environment isolation automatically - no need for separate local databases.
+
+### 4-Layer Data Model
+
+See `models/README.md` for detailed architecture documentation:
+
+1. **Raw** - Immutable source data
+2. **Staging** - Schema, types, basic cleansing
+3. **Cleaned** - Business logic, integration
+4. **Serving** - Analytics-ready (facts, dimensions, aggregates)
+
+## Configuration
+
+**Config:** `config.yaml`
+- DuckDB in-memory with R2 Iceberg catalog
+- Extensions: httpfs, iceberg
+- Auto-apply enabled (no prompts)
+- Initialization hooks for R2 secret/catalog attachment
+
+## Commands
+
+```bash
+# Plan changes for dev environment
+sqlmesh plan dev_yourname
+
+# Plan changes for prod
+sqlmesh plan prod
+
+# Run tests
+sqlmesh test
+
+# Validate models
+sqlmesh validate
+
+# Run audits
+sqlmesh audit
+
+# Format SQL files
+sqlmesh format
+
+# Start web UI
+sqlmesh ui
+```
+
+## Environment Variables (Prod)
+
+Required for production R2 Iceberg catalog:
+- `CLOUDFLARE_API_TOKEN` - R2 API token
+- `ICEBERG_REST_URI` - R2 catalog REST endpoint
+- `R2_WAREHOUSE_NAME` - Warehouse name (default: "materia")
+
+These are injected via Pulumi ESC (`beanflows/prod`) on the supervisor instance.
+
+## Development Workflow
+
+1. Make changes to models in `models/`
+2. Test locally: `sqlmesh test`
+3. Plan changes: `sqlmesh plan dev_yourname`
+4. Review and apply changes
+5. Commit and push to trigger CI/CD
+
+SQLMesh will handle environment isolation, table versioning, and incremental updates automatically.

transform/sqlmesh_materia/config.yaml

@@ -1,18 +1,8 @@
 # --- Gateway Connection ---
+# Single gateway connecting to R2 Iceberg catalog
+# Local dev uses virtual environments (e.g., dev_<username>)
+# Production uses the 'prod' environment
 gateways:
-
-  dev:
-    connection:
-      # For more information on configuring the connection to your execution engine, visit:
-      # https://sqlmesh.readthedocs.io/en/stable/reference/configuration/#connection
-      # https://sqlmesh.readthedocs.io/en/stable/integrations/engines/duckdb/#connection-options
-      type: duckdb
-      database: materia_dev.db
-      extensions:
-        - name: zipfs
-        - name: httpfs
-        - name: iceberg
-
   prod:
     connection:
       type: duckdb
@@ -21,8 +11,7 @@ gateways:
         - name: httpfs
         - name: iceberg
 
-
-default_gateway: dev
+default_gateway: prod
 
 # --- Hooks ---
 # Run initialization SQL before all plans/runs