feat(claude-plugin): restructure skills and add themed-button, themed-alert, themed-snackbar; fix ThemedColorPicker bugs

[PHKenny]

📋 Summary

• Migrates Claude Code plugin skills from .claude-plugin/skills/ (monolithic per-group files) to .claude/skills/ (one skill per widget with SKILL.md + references/api.md), matching the new marketplace format.
• Adds three new skills: themed-button, themed-alert, and themed-snackbar.
• Fixes several bugs in ThemedColorPicker and adds comprehensive widget tests.
• Updates LICENSE year, README with plugin installation instructions.

✨ Features

• Added themed-button skill: covers ThemedButton primary constructor, all 12 ThemedButtonStyle variants, six semantic factories (.save, .cancel, .info, .show, .edit, .delete), cooldown, long-press, and ThemedActionsButtons companion.
• Added themed-alert skill: covers ThemedAlert with all six ThemedAlertType severities, five ThemedAlertStyle surface treatments, and the ThemedAlertIcon companion.
• Added themed-snackbar skill: covers ThemedSnackbarMessenger setup, ThemedSnackbar data class, .of/.maybeOf accessors, queuing/stacking behavior, and deprecation guidance for width/maxLines.

🐛 Fixes

• Fixed ThemedColorPicker double # prefix bug: .hex extension already includes #, so the controller was showing ##RRGGBB.
• Fixed ThemedColorPicker TextEditingController memory leak: controller is now disposed in dispose().
• Fixed ThemedColorPicker external value not reflected: added didUpdateWidget to sync _value and controller text when parent passes a new value.
• Fixed ThemedColorPicker duplicate dialog buttons: removed conflicting manual Row of ThemedButton.cancel/.save while ColorPickerActionButtons already rendered its own buttons.
• Fixed ThemedColorPicker XOR assertion: replaced ambiguous || condition with != (XOR) and added a descriptive error message.
• Fixed ThemedColorPicker doc comment misalignment for onChanged, value, and disabled fields.
• Removed unused prefixIcon parameter from ThemedColorPicker.
• Fixed placeholder, dense, and padding forwarding to ThemedTextInput inside ThemedColorPicker.

📚 Docs

• Restructured Claude Code plugin: old .claude-plugin/skills/ monolithic files removed; replaced by per-widget skills under .claude/skills/ with split SKILL.md + references/api.md.
• Updated plugin.json to new marketplace schema and skill list.
• Updated README.md with Claude Code plugin installation instructions.
• Updated LICENSE copyright year to 2023-2026.
• Added comprehensive widget tests for ThemedColorPicker (rendering, disabled state, lifecycle, didUpdateWidget).

🤖 Generated with Claude Code

[github-actions]

📋 Changelog Summary

This PR includes the following changes:

🐛 Bug Fixes

• fix bugs, add tests and skill documentation (dccf712 by Manuel romero)

📚 Documentation

• add themed-button, themed-alert and themed-snackbar skills (78e6272 by @PHKenny, Claude Sonnet 4.6)
• update LICENSE year, README plugin section and pubspec.lock (388af86 by @PHKenny, Claude Sonnet 4.6)

📊 Diff Stats

Metric	Count
📄 Files changed	94
🟢 Insertions	$\color{green}\textsf{+9000}$
🔴 Deletions	$\color{red}\textsf{-5146}$

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[github-actions]

📊 Test Coverage Report

🎯 Dart/Flutter

Metric	Value
Coverage	16.4%
Lines covered	10859 / 127
Lines missing	-10732

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