## Summary
`agnes query "DESCRIBE unit_economics"` (where `unit_economics` is `query_mode='remote'`) previously returned DuckDB's nearest-name suggestion (`Did you mean "order_economics"`?), sending users down the wrong path. Now appends a friendly hint about remote tables.
Reproduced from a real analyst session — colleague spent ~30s diagnosing what was actually "this is a remote table, not materialized locally".
## Test plan
- [x] New test: `_query_local("DESCRIBE unit_economics", ...)` against an empty local DuckDB triggers the new hint, original DuckDB error still echoed.
- [x] Negative test: a syntax-error query does NOT trigger the hint (regex only matches "Table with name X does not exist").
- [x] `pytest tests/test_cli_query*.py` clean.
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