feat: add custom elements manifest generator

[codegangsta]

Description

Adds a Custom Elements Manifest (CEM) generator for Pine web components, following the CEM v1.0.0 specification. This replaces the previous VS Code HTML Custom Data generator with a standardized format that's supported by more tooling.

Why CEM?

• Broader editor support out of the box - JetBrains IDEs (WebStorm, IntelliJ) natively consume CEM files without any extensions. VS Code-based editors can use the wc-toolkit extension.
• No patching required - The previous implementation required a postinstall script to patch VS Code settings, which was fragile and invasive. CEM is a standard format that tools discover automatically via the customElements field in package.json.
• Cleaner implementation - Single generator, single output format, no runtime patching scripts.

Key changes:

• Created custom-elements-manifest-generator.ts - a custom Stencil output target that generates a CEM-compliant manifest
• Rich documentation extracted from MDX files including descriptions, examples, slots, CSS parts, and events
• Example links pointing to specific Storybook documentation sections
• Source links to GitHub for each component
• Added wc.config.js for local development with the wc-toolkit VS Code extension

Removed:

• vscode-custom-data-generator.ts - replaced by CEM
• vscode-settings-patcher.cjs - no longer needed
• Postinstall scripts that patched VS Code settings

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

• tested manually
• other: Verified CEM schema compliance, tested autocomplete in VS Code/Cursor with wc-toolkit extension

Test Configuration:

• Pine versions: 3.11.1
• OS: macOS
• Browsers: N/A (build tooling)
• Misc: VS Code with wc-toolkit.web-components-language-server extension

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes
• Design has QA'ed and approved this PR

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