Scala 3 Syntax Skill (3.8.x, strict profile)

Covers modern Scala 3 syntax, assuming the strict compiler profile documented in references/compiler-flags.md:

• Scala 3.8.4
• -source:future — selects the newest source dialect; warns on the old given / context-bound syntax from Scala 3.0–3.5, so the SIP-64 syntax below is the only syntax to emit.
• -preview — enables officially-released preview features (e.g. into).
• -language:strictEquality — == / != are only allowed between types that derives CanEqual (or via a given CanEqual).
• -Yexplicit-nulls — reference types are non-nullable; nullability is T | Null.
• A battery of -W* warnings surfaced by default (warnings, not hard errors — no -Xfatal-warnings — but treat each as a real issue to fix).