feat(hub-guide): language-agnostic auto-trigger across all skills

- Add principle 27: 'Language-Agnostic Auto-Trigger' to engineering-principles
- Remove hardcoded English-only keyword lists from all 26 skill descriptions
- Replace with concept-based detection: triggers from code context, project files,
  and file types regardless of spoken language
- Update detect-project.sh hook output with language-agnostic message

skills/rust/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: rust
-description: Rust best practices — ownership, error handling, async, project structure, clippy rules, testing, and idiomatic Rust. Use when writing Rust code, reviewing Rust projects, or whenever the user mentions "Rust," "cargo," "clippy," "ownership," "borrowing," "lifetimes," "Result," "Option," "async/await," "tokio," "Axum," "SeaORM," or "unsafe."
+description: Rust best practices — ownership, error handling, async, project structure, clippy rules, testing, and idiomatic Rust. Use when writing Rust code, reviewing Rust projects. Triggers when working with this language's files, regardless of spoken language."
 ---
 
 # Rust Best Practices