feat: add data-platform plugin (v4.0.0)

Add new data-platform plugin for data engineering workflows with:

MCP Server (32 tools):
- pandas operations (14 tools): read_csv, read_parquet, read_json,
  to_csv, to_parquet, describe, head, tail, filter, select, groupby,
  join, list_data, drop_data
- PostgreSQL/PostGIS (10 tools): pg_connect, pg_query, pg_execute,
  pg_tables, pg_columns, pg_schemas, st_tables, st_geometry_type,
  st_srid, st_extent
- dbt integration (8 tools): dbt_parse, dbt_run, dbt_test, dbt_build,
  dbt_compile, dbt_ls, dbt_docs_generate, dbt_lineage

Plugin Features:
- Arrow IPC data_ref system for DataFrame persistence across tool calls
- Pre-execution validation for dbt with `dbt parse`
- SessionStart hook for PostgreSQL connectivity check (non-blocking)
- Hybrid configuration (system ~/.config/claude/postgres.env + project .env)
- Memory management with 100k row limit and chunking support

Commands: /initial-setup, /ingest, /profile, /schema, /explain, /lineage, /run
Agents: data-ingestion, data-analysis

Test suite: 71 tests covering config, data store, pandas, postgres, dbt tools

Addresses data workflow issues from personal-portfolio project:
- Lost data after multiple interactions (solved by Arrow IPC data_ref)
- dbt 1.9+ syntax deprecation (solved by pre-execution validation)
- Ungraceful PostgreSQL error handling (solved by SessionStart hook)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

mcp-servers/data-platform/README.md

@@ -0,0 +1,131 @@
+# Data Platform MCP Server
+
+MCP Server providing pandas, PostgreSQL/PostGIS, and dbt tools for Claude Code.
+
+## Features
+
+- **pandas Tools**: DataFrame operations with Arrow IPC data_ref persistence
+- **PostgreSQL Tools**: Database queries with asyncpg connection pooling
+- **PostGIS Tools**: Spatial data operations
+- **dbt Tools**: Build tool wrapper with pre-execution validation
+
+## Installation
+
+```bash
+cd mcp-servers/data-platform
+python -m venv .venv
+source .venv/bin/activate  # On Windows: .venv\Scripts\activate
+pip install -r requirements.txt
+```
+
+## Configuration
+
+### System-Level (PostgreSQL credentials)
+
+Create `~/.config/claude/postgres.env`:
+
+```env
+POSTGRES_URL=postgresql://user:password@host:5432/database
+```
+
+### Project-Level (dbt paths)
+
+Create `.env` in your project root:
+
+```env
+DBT_PROJECT_DIR=/path/to/dbt/project
+DBT_PROFILES_DIR=/path/to/.dbt
+DATA_PLATFORM_MAX_ROWS=100000
+```
+
+## Tools
+
+### pandas Tools (14 tools)
+
+| Tool | Description |
+|------|-------------|
+| `read_csv` | Load CSV file into DataFrame |
+| `read_parquet` | Load Parquet file into DataFrame |
+| `read_json` | Load JSON/JSONL file into DataFrame |
+| `to_csv` | Export DataFrame to CSV file |
+| `to_parquet` | Export DataFrame to Parquet file |
+| `describe` | Get statistical summary of DataFrame |
+| `head` | Get first N rows of DataFrame |
+| `tail` | Get last N rows of DataFrame |
+| `filter` | Filter DataFrame rows by condition |
+| `select` | Select specific columns from DataFrame |
+| `groupby` | Group DataFrame and aggregate |
+| `join` | Join two DataFrames |
+| `list_data` | List all stored DataFrames |
+| `drop_data` | Remove a DataFrame from storage |
+
+### PostgreSQL Tools (6 tools)
+
+| Tool | Description |
+|------|-------------|
+| `pg_connect` | Test connection and return status |
+| `pg_query` | Execute SELECT, return as data_ref |
+| `pg_execute` | Execute INSERT/UPDATE/DELETE |
+| `pg_tables` | List all tables in schema |
+| `pg_columns` | Get column info for table |
+| `pg_schemas` | List all schemas |
+
+### PostGIS Tools (4 tools)
+
+| Tool | Description |
+|------|-------------|
+| `st_tables` | List PostGIS-enabled tables |
+| `st_geometry_type` | Get geometry type of column |
+| `st_srid` | Get SRID of geometry column |
+| `st_extent` | Get bounding box of geometries |
+
+### dbt Tools (8 tools)
+
+| Tool | Description |
+|------|-------------|
+| `dbt_parse` | Validate project (pre-execution) |
+| `dbt_run` | Run models with selection |
+| `dbt_test` | Run tests |
+| `dbt_build` | Run + test |
+| `dbt_compile` | Compile SQL without executing |
+| `dbt_ls` | List resources |
+| `dbt_docs_generate` | Generate documentation |
+| `dbt_lineage` | Get model dependencies |
+
+## data_ref System
+
+All DataFrame operations use a `data_ref` system to persist data across tool calls:
+
+1. **Load data**: Returns a `data_ref` string (e.g., `"df_a1b2c3d4"`)
+2. **Use data_ref**: Pass to other tools (filter, join, export)
+3. **List data**: Use `list_data` to see all stored DataFrames
+4. **Clean up**: Use `drop_data` when done
+
+### Example Flow
+
+```
+read_csv("data.csv") → {"data_ref": "sales_data", "rows": 1000}
+filter("sales_data", "amount > 100") → {"data_ref": "sales_data_filtered"}
+describe("sales_data_filtered") → {statistics}
+to_parquet("sales_data_filtered", "output.parquet") → {success}
+```
+
+## Memory Management
+
+- Default row limit: 100,000 rows per DataFrame
+- Configure via `DATA_PLATFORM_MAX_ROWS` environment variable
+- Use chunked processing for large files (`chunk_size` parameter)
+- Monitor with `list_data` tool (shows memory usage)
+
+## Running
+
+```bash
+python -m mcp_server.server
+```
+
+## Development
+
+```bash
+pip install -e ".[dev]"
+pytest
+```