Modernize highlight capture names to align with nvim-treesitter conventions (v0.5.0)

[aldoborrero]

Context

PR #32 fixed the No handler for is-not? error that nvim-treesitter users were hitting (see #12). But PerchunPak's follow-up comment on that issue highlighted a deeper divergence: nvim-treesitter vendors its own Nix queries because our capture names don't match nvim-treesitter's current conventions. Nvim-treesitter is now archived (2026-04-03), so those vendored queries are frozen and won't track future grammar updates.

Aligning our capture names with the modern tree-sitter conventions (used by nvim-treesitter, Helix, Zed, and most current tree-sitter theme ecosystems) means:

• Modern themes (Tokyo Night, Catppuccin, Gruvbox-Material, etc.) highlight Nix out-of-box without per-theme mappings.
• When a post-archival Neovim integration picks up Nix queries, ours plug in directly — no vendoring gap.
• Theme authors have one set of captures to target.

Proposed rename table

Current	v0.5.0
@escape	@string.escape
@string.special.uri	@string.special.url
@keyword (flat) for if, then, else	@keyword.conditional
@keyword (flat) for or (in select-default)	@keyword.operator
@keyword for let, inherit, in, rec, with, assert	@keyword (unchanged)
(missing) on (comment)	add @spell so nvim triggers spellcheck
@variable.builtin for true, false	@boolean
@variable.builtin for null	@constant.builtin
@variable.builtin for builtins, __currentSystem, etc.	@variable.builtin (unchanged)
@embedded inside (interpolation)	drop (let the injected language's theme take over)
@property (attrset keys, select attrs, binding lhs)	consider @variable.member (some conventions use this for attrset keys) — needs evaluation

Files to touch

• queries/highlights.scm — capture renames (~15-20 lines).
• test/highlight/basic.nix — update every # ^ <capture> annotation that references a renamed capture (63 assertions; many will NOT need changes since only the affected ones move).
• docs/highlight-groups.md — regenerate the reference list.
• CHANGELOG.md — section under v0.5.0 "Changed (breaking for some theme consumers)".

Why v0.5.0 and not v0.4.0

This is strictly breaking for consumers who string-map capture names (older themes, custom editor configs). v0.4.0 is intended as a purely additive / non-breaking release (bindings, fixes, doc-comment split). The modernization rightfully lives in a separate minor bump so downstream has a clear upgrade signal.

Out of scope for this issue

• Changing any grammar rule or node type (pure query work).
• Adding new queries (e.g. folds.scm) — covered separately.

Verification plan

• tree-sitter test — all 63 (or however many after this lands) highlight assertions pass against the new annotations.
• Eyeball the output of tree-sitter highlight on a representative Nix file to confirm nvim-treesitter-like coloring.

References

• PerchunPak's comment on Error: No handler for is-not? #12: Error: No handler for is-not? #12 (comment)
• Nvim-treesitter's vendored Nix queries (for comparison): https://github.com/nvim-treesitter/nvim-treesitter/tree/main/runtime/queries/nix
• nvim-treesitter highlight capture conventions
• tree-sitter-core highlight name conventions