Add IRIS as a new agent-driven database type with:
- iris:// connection URL scheme (default port 1972, user _SYSTEM)
- JDBC driver via agent (com.intersystems.jdbc.IRISDriver)
- Oracle-compatible DDL dialect and schema-aware SQL dialect
- Capability sets: schema-aware, tree schema, diagram, search, table structure
Closes#368
DuckDB was not recognized as a schema-aware database, so only the
default "main" schema was shown in the object tree and schema selector.
Added DuckDB to schema-aware type lists, implemented schema listing via
information_schema.schemata, and replaced hardcoded table_schema = 'main'
with parameterized queries.
t8y2