fix: Address mechanical review findings (security, performance, code hygiene)

[mingjerli]

Summary

Addresses 6 mechanical fixes identified during a staff engineer review of the clgraph codebase:

• Item 1 (Security): Fix Jinja2 SSTI vulnerability by replacing jinja2.Template with SandboxedEnvironment in multi_query.py
• Item 2 (Dependencies): Remove unused cloudpickle from core dependencies
• Item 3 (Code hygiene): Replace all print() calls with structured logging module usage; strip emoji from log messages
• Item 4 (Performance): Replace list.pop(0) (O(n)) with collections.deque.popleft() (O(1)) across 11 BFS traversals in 5 files
• Item 5 (Performance): Add edge adjacency indices (_outgoing_index/_incoming_index) to ColumnLineageGraph and PipelineLineageGraph for O(1) edge lookups instead of O(E) linear scans; cache _build_column_dependencies()
• Item 6 (Error handling): Narrow all 17 except Exception catches to specific exception types (SqlglotError, KeyError, ValueError, etc.); add debug-level logging at boundary handlers

Files changed (15)

File	Changes
multi_query.py	SSTI fix (Item 1)
pyproject.toml / uv.lock	Remove cloudpickle (Item 2)
pipeline.py	Logging, deque, adjacency indices, exception narrowing (Items 3-6)
execution.py	Logging, exception narrowing (Items 3, 6)
agent.py	Logging, exception narrowing (Items 3, 6)
column.py	Deque, adjacency indices, exception narrowing (Items 4-6)
models.py	Deque, adjacency indices (Items 4-5)
lineage_builder.py	Deque, exception narrowing (Items 4, 6)
visualizations.py	Deque, exception narrowing (Items 4, 6)
table.py	Exception narrowing (Item 6)
__init__.py	Exception narrowing (Item 6)
mcp/server.py	Logging, exception narrowing (Items 3, 6)
tools/sql.py	Exception narrowing (Item 6)
tests/test_validation_framework.py	Update 2 tests to check log records instead of stdout

Test plan

• All 778 tests pass (40 skipped - optional Dagster dependency)
• ruff check and ruff format pass
• Verify SandboxedEnvironment blocks SSTI payloads like {{ ''.__class__.__mro__[1].__subclasses__() }}
• Verify logging.basicConfig(level=logging.INFO) shows pipeline progress
• Spot-check adjacency index correctness on enterprise demo pipeline