chore: Restore broader version constraints for pinned dependencies after uv migration

## Summary

During the migration from Poetry to uv (PR #945), several dependencies were pinned to specific versions to match the poetry.lock file and ensure compatibility. These should be restored to broader version constraints after verifying compatibility.

**Requested by:** @aaronsteers

## Dependencies to Review

### 1. DuckDB and DuckDB-Engine
**Current (pinned):**
```toml
"duckdb==1.4.3", # Pinned to match poetry.lock
"duckdb-engine==0.17.0", # Pinned to match poetry.lock
```

**Target (broader constraints):**
```toml
"duckdb>=1.4.0,<2.0",
"duckdb-engine>=0.17.0,<1.0",
```

### 2. SQLAlchemy
**Current (pinned):**
```toml
"sqlalchemy==2.0.43", # Pinned to match poetry.lock
```

**Target (broader constraints):**
```toml
"sqlalchemy>=1.4.51,!=2.0.36,<3.0",
```

## Context

These dependencies were pinned because the uv resolver picked different versions than Poetry did, which caused test failures (specifically a DuckDB/SQLAlchemy compatibility issue with `pg_collation` table). Pinning to the exact versions from poetry.lock resolved the issue.

## Acceptance Criteria

- [ ] Test with broader version constraints to verify compatibility
- [ ] If tests pass, restore the broader constraints
- [ ] If tests fail, document the specific version incompatibilities and determine if the pins should remain

## Related

- PR #945: ci: migrate from Poetry to uv package manager