Add strict YAML localization catalogs

[gregjotau]

Summary

• replace .properties bundles with locale-directory YAML catalogs under src/main/resources/i18n
• add named message arguments plus compile-time _plural and _select patterns
• generate locale selection and message branches directly into renderers
• configure default and supported BCP 47 locales through the Gradle plugin
• migrate the example and document the strict catalog profile

Safety and runtime model

• uses the YAML 1.2 failsafe schema so every scalar remains text
• rejects duplicate keys, tags, anchors, aliases, sequences, multiple documents, unsupported locales, unreachable plural categories, and locale key or argument drift
• checks plural/select argument types against page-model properties and validates enum variants
• keeps SnakeYAML Engine on the compiler path only; request-time rendering has no catalog parser or lookup engine
• embeds integer cardinal rules derived from Unicode CLDR 49 and evaluates the effective catalog locale, including default fallback

Breaking changes

• message catalogs now use .yaml; Java properties bundles are no longer loaded
• template arguments are named, for example #{home.title(version=${version})}
• the default catalog directory is src/main/resources/i18n

Verification

• ./gradlew build --console=plain
• compiler tests cover strict YAML behavior, locale parity, named arguments, plural/select structures, and invalid inputs
• runtime tests cover representative CLDR categories and unsupported locales
• the migrated English/Norwegian example compiles its generated renderer successfully