Add update-tokens skill (#2543)

* Add update-tokens skill

* Changes in editing rules

* Simplify specific rules

* Force schema updates

Author: aweell

.github/skills/update-tokens/SKILL.md

@@ -0,0 +1,116 @@
+---
+name: update-tokens
+description: Edit Mistica token JSON files when the user requests new tokens, color, spacing, text, radius, changes in skin, or new brand tokens or skins.
+---
+
+# Token Editor
+
+This skill is used to modify Mistica design tokens JSON files in a controlled and consistent way.
+
+---
+
+## When to use
+
+Use this skill **only** when the user explicitly requests:
+
+- Adding a new token
+- Editing an existing token
+- Creating a new brand / skin
+- Modifying token values or descriptions
+
+Do not use this skill for:
+
+- UI implementation
+- Token usage in application code
+- Guessing, proposing, or inventing new tokens without explicit request
+
+### Execution flow
+
+When this skill is invoked, follow this order strictly:
+
+1. Identify the exact user request (token name, type, brand)
+2. Locate the affected files:
+   - Brand file(s)
+   - Schema file (if adding or removing tokens)
+   - contrastPairs.js (if color tokens affect contrast)
+3. Apply the minimal required change
+4. Validate structure consistency across brands
+5. Update schema file
+6. Update linter if impacted
+7. Summarize the changes made
+
+---
+
+## Token file structure
+
+- Tokens live in the `tokens/` directory
+- Brand files are named: `<brand>.json`
+- Schema file: `tokens/schema/skin-schema.json`
+- Linter contrast pairs live in `tokens/linter/contrastPairs.js`
+
+Each brand file must define **the same token structure**:
+
+- `light`
+- `dark`
+- `radius`
+- `text`
+- `spacing`
+- `themeVariant`
+- `componentProperties`
+
+May differ between brands:
+
+- Token values
+- `global.palette` definitions
+
+Token **keys and structure must always match across brands**.
+
+---
+
+## Editing rules (mandatory)
+
+### General
+
+- Never invent tokens not requested by the user
+- Do not create new token types unless explicitly specified by the user
+- Never remove existing tokens unless explicitly requested
+- Keep JSON formatting consistent with existing files
+- Apply **minimal diffs**: change only what is required
+- Do not reorder unrelated tokens
+- All brand failes should follow the structure enforced in `tokens/schema/skin-schema.json`
+
+---
+
+## Adding or editing tokens
+
+### Color tokens
+
+- Must exist in **both** `light` and `dark`
+- Values must reference `global.palette`, if the have alpha `rgba({global.palette}, alphaValue)`
+- Token `description` must exactly match the palette reference
+- Do not use raw hex, rgb, or rgba values
+- Insert new tokens after the closest existing token name (alphabetical proximity)
+
+---
+
+### Text tokens
+
+- A new `text.size` token **must** also define `text.lineHeight`
+
+## Schema updates
+
+- The schema file **must** be updated when new tokens are added
+- Schema structure must exactly match the brand token structure
+- New `global.palette` tokens must be added per brand and included under the corresponding pattern in `definitions/constantProperties/patternProperties`
+- Do not modify schema entries unrelated to the change
+
+---
+
+## Linter contrastPairs updates
+
+- Update existent or create a new contrast pair if needed
+
+Do not update contrast pairs for:
+
+- Media-specific tokens
+- Tokens using alpha