fix(security): preserve UTF-8 SQL parser offsets - #181

Summary

• derive SQL byte offsets only from the original input string
• centralize ASCII case-insensitive forward, reverse, keyword, and literal-aware scanning
• repair affected typed DDL, Control Plane, protocol, trigger, and graph parser paths
• add expanding-Unicode regressions and persistent-connection protocol coverage

Validation

• cargo nextest run -p nodedb-sql --no-fail-fast (728 passed)
• cargo nextest run -p nodedb --lib --no-fail-fast (4299 passed)
• focused pgwire RETURNING, SQL PREPARE, cursor, and native SET/SHOW integration regressions
• cargo clippy --all-targets --all-features -- -D warnings
• cargo fmt --all --check
• git diff --check
• exhaustive static security review: pass
• regression coverage and layout review: pass