chore: add debug-widget Claude Code skill

[rahmanunver]

Pull request type

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Description

Adds .claude/skills/debug-widget/ — a Claude Code skill for debugging Mendix pluggable widgets.

Why: Widget bugs in this repo follow repeatable patterns (stale state, layout regressions, data not updating). Without a shared process each session re-discovers the same things: which page to open, how to find widget selectors, how the Gate/MobX reactive chain works. This skill encodes that knowledge once.

Core constraint: reproduce the bug with a Playwright script before reading source code; verify the fix with the same script before claiming success.

Files added:

File	Purpose
SKILL.md	4-phase loop: Reproduce → Analyze+Fix → Build+Deploy → Verify
diagnostic-patterns.md	Playwright script templates by bug category (Layout, Data, Stale State, Interaction, Performance)
page-discovery.md	Tier 0–3 page discovery from live app → URL → XML grep → Playwright crawl
reactive-chain.md	Simple vs. DI+MobX architecture tiers, trace procedure, key files for datagrid-web

Example: WC-3355 (combobox value not updating externally) — skill drove writing a Stale State diagnostic script, tracing the issue to combobox-web's hook not reacting to external attribute changes, and verifying the fix via Playwright before declaring success.