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>

plugins/data-platform/commands/run.md

@@ -0,0 +1,55 @@
+# /run - Execute dbt Models
+
+Run dbt models with automatic pre-validation.
+
+## Usage
+
+```
+/run [model_selection] [--full-refresh]
+```
+
+## Workflow
+
+1. **Pre-validation** (MANDATORY):
+   - Use `dbt_parse` to validate project
+   - Check for deprecated syntax (dbt 1.9+)
+   - If validation fails, show errors and STOP
+
+2. **Execute models**:
+   - Use `dbt_run` with provided selection
+   - Monitor progress and capture output
+
+3. **Report results**:
+   - Success/failure status per model
+   - Execution time
+   - Row counts where available
+   - Any warnings or errors
+
+## Examples
+
+```
+/run                           # Run all models
+/run dim_customers             # Run specific model
+/run +fct_orders               # Run model and its upstream
+/run tag:daily                 # Run models with tag
+/run --full-refresh            # Rebuild incremental models
+```
+
+## Selection Syntax
+
+| Pattern | Meaning |
+|---------|---------|
+| `model_name` | Run single model |
+| `+model_name` | Run model and upstream |
+| `model_name+` | Run model and downstream |
+| `+model_name+` | Run model with all deps |
+| `tag:name` | Run by tag |
+| `path:models/staging` | Run by path |
+
+## Available Tools
+
+Use these MCP tools:
+- `dbt_parse` - Pre-validation (ALWAYS RUN FIRST)
+- `dbt_run` - Execute models
+- `dbt_build` - Run + test
+- `dbt_test` - Run tests only