feat: add color scheme customization

[kantord]

No description provided.

[Copilot]

Pull request overview

Adds operator-configurable color scheme branding so the Electron main process can load a JSON theme, serialize allowed color tokens to CSS, and expose it to the renderer before React mounts.

Changes:

• Adds branding config schema, token sanitization/serialization utilities, loader, and tests.
• Passes generated branding CSS from main to preload via additionalArguments, then injects it in the renderer.
• Adds a sample test theme, documentation, and a dev launch script for custom-theme verification.

Reviewed changes

Copilot reviewed 49 out of 49 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
common/branding/color-tokens.ts	Defines allowed color tokens and serializes safe overrides to CSS.
common/branding/__tests__/color-tokens.test.ts	Tests token filtering, sanitization, and CSS output.
common/branding/schema.ts	Defines the branding JSON schema.
main/src/branding/load.ts	Loads branding config and converts color tokens to CSS.
main/src/branding/__tests__/load.test.ts	Tests config loading, invalid inputs, and CSS generation.
main/src/branding/paths.ts	Resolves the branding config path.
main/src/main-window.ts	Loads branding CSS and passes it to the renderer process.
preload/src/api/branding.ts	Reads and decodes branding CSS from process arguments.
preload/src/api/__tests__/branding.test.ts	Tests preload branding argument handling.
preload/src/preload.ts	Exposes the branding API through electronAPI.
renderer/src/renderer.tsx	Injects branding CSS before mounting React.
renderer/src/index.css	Adds additional themeable color variables.
renderer/src/common/mocks/electronAPI.ts	Adds branding to the renderer test Electron API mock.
vitest.setup.ts	Adds branding to the global Electron API test stub.
branding-examples/README.md	Documents branding examples and usage.
branding-examples/test-theme.json	Adds a sample custom color theme.
scripts/start-custom-theme.ts	Adds a helper for launching with the sample theme.
package.json	Adds the start:customTheme script.