test: add comptime smoke checks

[forketyfork]

Motivation

• Add a lightweight, dedicated compile-time smoke suite to detect regressions in helpers that are expected to remain evaluable at comptime, such as configuration color parsing and grid/layout math.
• Ensure invariants used by generated/comptime code (colors, palette lookup, grid dimension calculations, and index/position math) are checked proactively during CI/test runs.
• Provide a convenient place to extend comptime coverage for future pure helpers without conflating those checks with runtime tests.

Description

• Add src/comptime_checks.zig, a test root containing comptime-scoped checks for Color.fromHex, ThemeConfig fallback getters, PaletteConfig.getColor, GridLayout.calculateDimensions bounds, and GridPosition index/position mapping.
• Wire the new suite into the build by adding a comptime_checks_mod in build.zig, importing the shared toml module where needed, and adding the module to zig build test as a test artifact so it runs alongside the existing application and MCP unit tests.
• Update docs/development.md to document that zig build test now runs the compile-time smoke suite and guidance on when to extend it.

Testing

• Ran git diff --check which passed (no whitespace/format issues reported).
• Attempted zig build and zig build test but these were not run because zig is not installed in this environment (so the new test target was not executed here).
• Attempted just lint / zig fmt via the dev shell but just/nix/zig were not available in the sandbox, so formatting/lint steps were not executed here.

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Codex Task

[Copilot]

Pull request overview

This PR adds a lightweight compile-time smoke test suite to ensure selected pure helpers remain usable during Zig comptime evaluation, and wires that suite into the existing zig build test workflow.

Changes:

• Adds src/comptime_checks.zig with compile-time checks for color parsing, theme/palette fallbacks, grid dimension invariants, and grid index/position mapping.
• Registers the new test root in build.zig and includes it in the test step.
• Documents the compile-time smoke suite in the development testing instructions.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/comptime_checks.zig	Adds dedicated comptime smoke tests for config and grid helper invariants.
build.zig	Creates and runs the new comptime checks test artifact as part of zig build test.
docs/development.md	Documents that zig build test includes the compile-time smoke suite and when to extend it.

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