Add --readonly CLI flag to prevent all write operations

[noxymon-mekari]

Summary

• Add --readonly CLI flag that acts as a hard safety toggle to prevent all write operations when connecting to databases
• Hide write tools from AI agent's tool list entirely in readonly mode (defense in depth)
• Reject write tool calls with a clear error message if called directly despite being hidden
• Fix SQLite path parsing to handle flags in any position (--readonly /path/to/db previously broke because args[0] picked up the flag instead of the path)

Motivation

AI agents using this MCP server can execute arbitrary write operations (INSERT, UPDATE, DELETE, CREATE/ALTER/DROP TABLE). When connecting to production or shared databases, users need a hard guarantee that no writes can occur regardless of what the
agent attempts.

How it works

# Append --readonly to any database command
node dist/src/index.js --readonly /path/to/database.db
node dist/src/index.js --readonly --postgresql --host localhost --database mydb

Write tools blocked in readonly mode:

┌────────────────┬────────────────────────────┐
│      Tool      │         Operation          │
├────────────────┼────────────────────────────┤
│ write_query    │ INSERT, UPDATE, DELETE     │
├────────────────┼────────────────────────────┤
│ create_table   │ CREATE TABLE               │
├────────────────┼────────────────────────────┤
│ alter_table    │ ALTER TABLE                │
├────────────────┼────────────────────────────┤
│ drop_table     │ DROP TABLE                 │
├────────────────┼────────────────────────────┤
│ append_insight │ INSERT (business insights) │
└────────────────┴────────────────────────────┘

Read-only tools always available:
read_query, export_query, list_tables, describe_table, list_insights

Defense in depth:
1. Write tools are removed from ListTools response — the AI agent never sees them
2. If a write tool is called directly anyway, it returns isError: true with a clear message