feat: add DQL format button to the query editor

[shaunpatterson]

What

A Format button next to Clear that pretty-prints the current query via a conservative, whitespace-only DQL formatter (lib/formatDql.js).

in:  {q(func: has(name)){name age friend{name}}}
out: {
       q(func: has(name)) {
         name
         age
         friend {
           name
         }
       }
     }

Formatter guarantees

• Whitespace-only: never reorders, quotes, or rewrites tokens.
• Tokenizer respects string literals (with escapes) and # comments — content inside strings is never touched; language tags (name@en:fr) stay merged.
• 2-space indent, { at line end, } dedented on its own line, one field per line; @filter(...)/arg groups stay attached to their field; as-var blocks and query headers stay on one line.
• N-Quad bodies inside set { } / delete { } mutation blocks are re-indented but otherwise left raw.
• Idempotent (format(format(x)) === format(x), tested); unterminated string → input returned unchanged; unbalanced braces degrade gracefully (depth clamped, no error).

Testing

14 unit tests covering all of the above. npm run build passes.

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