Initial duckdb skill with HTTP API

SKILL.md

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+---
+name: duckdb
+description: DuckDB embedded analytical database with HTTP API
+metadata:
+  version: "1.0.0"
+  vibestack:
+    main: false
+---
+
+# DuckDB Skill
+
+[DuckDB](https://duckdb.org/) - fast in-process analytical database with a simple HTTP API.
+
+## Features
+
+- Embedded OLAP database (no separate server process)
+- Query CSV, Parquet, JSON files directly
+- SQL interface via HTTP API
+- Persistent storage option
+- Auto-registers with Caddy if present
+
+## Configuration
+
+| Variable | Description | Default |
+|----------|-------------|---------|
+| `DUCKDB_PORT` | HTTP API port | `8432` |
+| `DUCKDB_DATABASE` | Database file path | `:memory:` |
+| `DUCKDB_DATA_DIR` | Directory for data files | `/data/duckdb` |
+| `DUCKDB_DOMAIN` | Domain for Caddy auto-config | (none) |
+| `DUCKDB_READ_ONLY` | Read-only mode | `false` |
+
+## HTTP API
+
+### Execute Query
+
+```bash
+# Simple query
+curl -X POST http://localhost:8432/query \
+  -H "Content-Type: application/json" \
+  -d '{"sql": "SELECT 1 + 1 AS result"}'
+
+# Query CSV file
+curl -X POST http://localhost:8432/query \
+  -d '{"sql": "SELECT * FROM read_csv_auto(\"/data/duckdb/sales.csv\") LIMIT 10"}'
+
+# Query Parquet file
+curl -X POST http://localhost:8432/query \
+  -d '{"sql": "SELECT * FROM read_parquet(\"/data/duckdb/events.parquet\")"}'
+```
+
+### Response Format
+
+```json
+{
+  "success": true,
+  "columns": ["result"],
+  "rows": [[2]],
+  "row_count": 1,
+  "time_ms": 0.5
+}
+```
+
+## Use Cases
+
+### Analytics on Log Data
+
+```sql
+-- Query JSON logs
+SELECT
+  json_extract_string(line, '$.level') as level,
+  count(*) as count
+FROM read_json_auto('/var/log/supervisor/*.log')
+GROUP BY level;
+```
+
+### Query Remote Data
+
+```sql
+-- Query remote Parquet (S3, HTTP)
+SELECT * FROM read_parquet('https://example.com/data.parquet');
+
+-- Query remote CSV
+SELECT * FROM read_csv_auto('https://example.com/data.csv');
+```
+
+### Create Persistent Tables
+
+```sql
+-- Create table
+CREATE TABLE events AS
+SELECT * FROM read_parquet('/data/duckdb/events.parquet');
+
+-- Query table
+SELECT date_trunc('hour', timestamp) as hour, count(*)
+FROM events
+GROUP BY 1 ORDER BY 1;
+```
+
+## CLI Access
+
+```bash
+# Interactive shell
+duckdb /data/duckdb/analytics.db
+
+# One-off query
+duckdb -c "SELECT * FROM 'data.csv' LIMIT 5"
+```
+
+## Extensions
+
+DuckDB supports extensions for additional functionality:
+
+```sql
+-- Install and load extensions
+INSTALL httpfs;
+LOAD httpfs;
+
+-- Now query S3/HTTP directly
+SELECT * FROM read_parquet('s3://bucket/data.parquet');
+```