Modified extract_loop_condition() to use ConditionEnv for variable lookup:
- Now returns ValueId instead of i64 for loop limit
- Uses lower_value_expression() for both literals and variables
- Integrated ConditionEnvBuilder in Pattern 3 if-sum path
This enables realistic loop patterns like `loop(i < len)` in if-sum.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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