feat: implement TextMate grammar catalog and language detection

[SSobol77]

Implement the TextMate grammar catalog used by ECLI syntax highlighting.

Scope:

• map file extension to language id
• map language id to TextMate grammar
• read grammar scopeName and grammar path
• support fallback for unknown files
• do not execute extension code

Done when:

• .py, .js, .ts, .json, .md, .rs, .c, .cpp are mapped deterministically
• malformed or missing grammar data is non-fatal
• tests cover representative grammars from src/ecli/extensions