#270 Define variable and form case sensitivity

[bsutton]

Summary

• define variable names and patterns as case-sensitive on every platform
• define form aliases and field identifiers as case-sensitive
• document Windows environment export considerations
• add API regression coverage for case-distinct variables, aliases, and fields

Validation

• cargo fmt --all -- --check
• cargo clippy --locked -p revault_lockbox_api@0.0.4 -p revault_cli --all-targets -- -D warnings
• cargo test --locked -p revault_lockbox_api@0.0.4 case_sensitive
• cargo test --locked -p revault_cli

Closes #270