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/lineage.md

@@ -0,0 +1,60 @@
+# /lineage - Data Lineage Visualization
+
+Show data lineage for dbt models or database tables.
+
+## Usage
+
+```
+/lineage <model_name> [--depth N]
+```
+
+## Workflow
+
+1. **Get lineage data**:
+   - Use `dbt_lineage` for dbt models
+   - For database tables, trace through dbt manifest
+
+2. **Build lineage graph**:
+   - Identify all upstream sources
+   - Identify all downstream consumers
+   - Note materialization at each node
+
+3. **Visualize**:
+   - ASCII art dependency tree
+   - List format with indentation
+   - Show depth levels
+
+4. **Report**:
+   - Full dependency chain
+   - Critical path identification
+   - Refresh implications
+
+## Examples
+
+```
+/lineage dim_customers
+/lineage fct_orders --depth 3
+```
+
+## Output Format
+
+```
+Sources:
+  └── raw_customers (source)
+  └── raw_orders (source)
+
+dim_customers (table)
+  ├── upstream:
+  │   └── stg_customers (view)
+  │       └── raw_customers (source)
+  └── downstream:
+      └── fct_orders (incremental)
+      └── rpt_customer_lifetime (table)
+```
+
+## Available Tools
+
+Use these MCP tools:
+- `dbt_lineage` - Get model dependencies
+- `dbt_ls` - List dbt resources
+- `dbt_docs_generate` - Generate full manifest