fix(queries): fold aggregate option values, highlight reserved names

[stefanvanburen]

Two query-only gaps, both left over from the query pass in #32. No grammar or parser changes.

block_lit was indentable but not foldable

#32 added block_lit as an indent.begin, but it was never added to folds.scm — so a multi-line aggregate option value indented correctly and then couldn't be folded. Every other brace-delimited body in the grammar is foldable.

Before, on a message containing a multi-line option value, the fold query captured the enclosing message and a nested enum but nothing for the option body. Now:

capture: fold, start: (1, 0), end: (7, 1)   ← message
capture: fold, start: (2, 21), end: (5, 3)  ← block_lit  (new)
capture: fold, start: (6, 2), end: (6, 19)  ← enum

reserved "foo"; had no highlight at all

Reserved names parse as reserved_identifier, which is its own node type rather than (string), so no rule matched them. Only the reserved keyword and the ; were captured — reserved names were the one literal in the grammar that rendered as plain unstyled text, while every other string in the file was highlighted.

(reserved_identifier) @string

Verification

tree-sitter test  →  38/38 parses, 0 failures, 70 highlight assertions

Three new highlight assertions cover the reserved-name case (67 → 70).

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