fix(edit): make move_symbol writes race-safe

[ScriptedAlchemy]

Summary

• reject destination symlink escapes and source/destination inode aliases
• preserve in-project symlinks while using atomic sibling-renames
• revalidate both file snapshots before the two-file commit and avoid clobbering concurrent rollback edits
• use cross-platform same-file identity for hard links

Verification

• cargo test --lib move_symbol (22 passed)
• cargo test --test mcp_suite move_symbol (13 passed)
• cargo clippy --all-targets --all-features -- -D warnings
• cargo fmt --check

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