refactor: Remove 2nd person from error messages

[max-sixty]

Summary

• Removed 2nd person pronouns (you/your) from all error messages
• Used softer modal verbs like "might" for hint messages to maintain a friendly tone
• Kept hard constraint errors as direct imperative statements (e.g., "X requires Y")
• Added error message style guidelines to CLAUDE.md

Changes

Error messages updated:

• lowering.rs: Changed hints to use "might be missing?" pattern
• ast_expand.rs: Changed to imperative statements for self-equality operator constraints
• resolver/types.rs: Changed function argument hint to use "might"
• CLAUDE.md: Added "Error Messages" section with style guidelines

Examples:

• ❌ "are you missing `from` statement?" → ✅ "`from` statement might be missing?"
• ❌ "did you forget to specify the column name?" → ✅ "column name might be missing?"
• ❌ "you can only use X" → ✅ "X requires Y"

Test plan

• All 611 integration tests pass
• All lints pass (prettier, ruff, cargo fmt, cargo clippy)
• JavaScript/TypeScript binding tests pass
• Python binding tests pass
• Snapshot tests reviewed and updated
• Documentation and playground builds successful

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