Unify WHERE pipeline on ExpressionNode, retire Evaluation, add .none()

[flyon]

Summary

This PR completes negation support in the query DSL by unifying all WHERE conditions on ExpressionNode and retiring the legacy Evaluation class. Added .none() collection quantifier for filtering where no elements match a condition.

Key Changes

WHERE Pipeline Unification

• Removed Evaluation class and its 4-stage pipeline (Evaluation → WherePath → DesugaredWhere → CanonicalWhere → IR)
• .equals() now returns ExpressionNode instead of Evaluation, enabling .not() chaining
• Simplified WhereClause type to accept only ExpressionNode or ExistsCondition (or callbacks returning them)
• Removed WhereEvaluationPath, DesugaredWhereComparison, DesugaredWhereBoolean, CanonicalWhereComparison, CanonicalWhereLogical, CanonicalWhereExists, CanonicalWhereNot types

New Collection Quantifier

• Added .none(fn) method on QueryShapeSet for "no elements match" filtering
• Generates FILTER(NOT EXISTS { ... }) in SPARQL
• Equivalent to .some(fn).not() but reads more naturally

Expression System Enhancements

• Added ExistsCondition type to represent collection quantifiers (.some(), .every(), .none())
• Added isExistsCondition() guard function
• Added tracedAliasExpression() for root shape comparisons
• Updated toExpressionNode() to handle context references and alias expressions

IR Simplification

• DesugaredWhere now only contains DesugaredExpressionWhere and DesugaredExistsWhere
• CanonicalWhereExpression simplified to only DesugaredExpressionWhere and DesugaredExistsWhere
• Removed lowerWhereArg() function (no longer needed)
• lowerWhere() now handles only expression and exists conditions

Test Coverage

• Added golden tests for .none(), .some().not(), .equals().not(), and chained negations
• Updated IR canonicalization tests to reflect new WHERE structure
• Updated IR desugar tests to remove Evaluation-related assertions

Implementation Details

The unification works by recognizing that ExpressionNode is already an IR representation, eliminating the need for intermediate transformation stages. Collection quantifiers (.some(), .every(), .none()) are handled separately via ExistsCondition, which lowers to IRExistsExpression with appropriate negation flags.

All negation now flows through two mechanisms:

1. Expression-level: .not() method on ExpressionNode for boolean negation
2. Pattern-level: ExistsCondition with negation for collection quantifiers

This enables natural chaining like p.name.equals('Alice').not() and p.friends.none(f => f.hobby.equals('Chess')).

https://claude.ai/code/session_019MDcpswuKKNx9YhC2S2vT7