Add VHDL-2008 syntax highlighting

[BuzzwordChief]

Adds basic syntax highlighting for VHDL-2008.

• New src/langs/vhdl.jai implemented in the same style as the C highlighter (src/langs/c.jai).
• Case-insensitive keywords (using equal_nocase over a compile-time entry list to avoid per-identifier allocations).
• File extension detection for .vhd, .vhdl
• Single-line comment toggling (--); block comments fall back to single-line.
• Added language sample for the color preview widget.
• Registered in the language enum, tokenizer dispatch, file type tables, and extension mapping.

Disclaimer: This was heavily vibe-coded.