feat(documentation/dees-heading): Add codex documentation overview and dees-heading component demo

codex.md

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+# Codex: Project Overview and Codebase Structure
+
+## Project Overview
+- Package: `@design.estate/dees-catalog`
+- Focus: Web Components library providing UI elements and layouts for modern web apps.
+
+## Directory Layout
+- ts_web/: TypeScript source files
+  - elements/: Individual Web Component definitions
+  - pages/: Page-level templates for composite layouts
+- html/: Demo/app entry point loading the bundled scripts
+- dist_bundle/: Bundled browser JS and source maps
+- dist_ts_web/: ES module outputs for TypeScript/web consumers
+- dist_watch/: Watch-mode development bundle with live reload
+- test/: Browser-based tests using `@push.rocks/tapbundle`
+
+## Component Patterns
+- Each component in ts_web/elements/:
+  - Decorated with `@customElement('tag-name')`
+  - Extends `DeesElement` from `@design.estate/dees-element`
+  - Uses `@property` for reactive, reflected attributes
+  - Defines `static styles = [cssManager.defaultStyles, css`...`]`
+  - Implements `render()` returning a Lit `html` template with slots or markup
+  - Exposes a demo via `public static demo` linking to `.demo.ts` files
+
+## Build & Development Workflow
+- Install dependencies: `npm install` or `pnpm install`
+- Build production bundle: `npm run build`
+- Start dev watch mode: `npm run watch`
+- Run tests: `npm test` (launches browser fixtures)
+
+## Theming & Utilities
+- Default global styles via `cssManager.defaultStyles`
+- Theme-aware values with `cssManager.bdTheme(light, dark)`
+- DOM utilities set up in `html/index.ts` using `@design.estate/dees-domtools`
+
+## Documentation
+- `readme.md` provides an overview of all components and basic usage
+- Live examples in `.demo.ts` files
+  accessible via component `demo` static property
+
+## Updates to this file
+If you have pattern insisights or general changes to the codebase, please update this file.