Add //color command for native color picking and hex insertion

[Copilot]

This adds a new slash command to let users pick a color and insert hex codes like #EDEDED directly into GitHub markdown textareas. The command is implemented as a setup-panel flow using a native color input plus editable hex value.

• Command behavior

  • Adds //color command registration and loading in the content script.
  • preflight() always opens a command-specific setup panel instead of grid/list results.
  • Inserts selected color as uppercase #RRGGBB; invalid manual input falls back to #EDEDED.

• UI + insertion flow

  • Setup panel includes:
    • native <input type="color">
    • hex text input (#RRGGBB)
    • Insert action
  • Pressing Enter in the hex field also inserts the normalized color.

• Tests

  • Adds focused unit tests for:
    • setup-panel preflight behavior
    • hex normalization
    • invalid-input fallback
    • insert callback wiring

• Docs

  • Adds command docs at docs/commands/color/README.md.
  • Updates command listings in docs/commands/README.md and top-level README.md.

const normalized = normalizeHexColor(hexInput.value)
insertTextAtCursor(normalized)
// e.g. "#00ff00" -> "#00FF00"

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add color picker command</issue_title>
<issue_description>Add a command that opens a color picker for then insert color codes like #EDEDED.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add color picker command #96

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[github-actions]

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Version: 0.0.6 | Build: PR#97@4068aba

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