Complete library cleanup and documentation overhaul

## Library Code Cleanup (~1,200+ lines removed)
- Remove legacy markdown system (markdown.js, previewer.js)
- Delete unused EditContext code from ui/editor.js (~400 lines)
- Remove version history UI components from form-renderer.js (~180 lines)
- Clean unused CSS styles from insertr.css (~120 lines)
- Update package.json dependencies (remove marked, turndown)

## Documentation Updates
- README.md: Update from markdown to HTML-first approach
- AGENTS.md: Add current architecture guidance and HTML-first principles
- TODO.md: Complete rewrite with realistic roadmap and current status
- demos/README.md: Update for development demo server usage

## System Reality Alignment
- All documentation now reflects current working system
- Removed aspirational features in favor of actual capabilities
- Clear separation between development and production workflows
- Accurate description of style-aware editor with HTML preservation

## Code Cleanup Benefits
- Simplified codebase focused on HTML-first approach
- Removed markdown conversion complexity
- Cleaner build process without unused dependencies
- Better alignment between frontend capabilities and documentation

Ready for Phase 3a server updates with clean foundation.

internal/content/assets/insertr.css

@@ -11,7 +11,7 @@
  * - .insertr-gate: Minimal styling for user-defined gates
  * - .insertr-auth-*: Authentication controls and buttons  
  * - .insertr-form-*: Modal forms and inputs
- * - .insertr-version-*: Version history modal
+ * - .insertr-style-aware-*: Style-aware editor components
  */
 
 /* =================================================================
@@ -546,133 +546,7 @@ body:not(.insertr-edit-mode) .insertr-editing-hover::after {
     color: var(--insertr-text-primary);
 }
 
-/* =================================================================
-   VERSION HISTORY MODAL
-   ================================================================= */
 
-.insertr-version-modal {
-    padding: var(--insertr-spacing-lg);
-    margin: 0;
-    font-family: var(--insertr-font-family);
-    font-size: var(--insertr-font-size-base);
-    line-height: var(--insertr-line-height);
-    color: var(--insertr-text-primary);
-    background: var(--insertr-bg-primary);
-}
-
-.insertr-version-header {
-    margin: 0 0 var(--insertr-spacing-lg) 0;
-    padding: 0 0 var(--insertr-spacing-md) 0;
-    border-bottom: 1px solid var(--insertr-border-color);
-}
-
-.insertr-version-title {
-    margin: 0 0 var(--insertr-spacing-sm) 0;
-    padding: 0;
-    font-size: var(--insertr-font-size-lg);
-    font-weight: 600;
-    color: var(--insertr-text-primary);
-}
-
-.insertr-version-help {
-    margin: 0;
-    padding: 0;
-    font-size: var(--insertr-font-size-sm);
-    color: var(--insertr-text-muted);
-}
-
-.insertr-version-list {
-    margin: 0 0 var(--insertr-spacing-lg) 0;
-    padding: 0;
-    max-height: 400px;
-    overflow-y: auto;
-}
-
-.insertr-version-item {
-    padding: var(--insertr-spacing-sm);
-    margin: 0 0 var(--insertr-spacing-sm) 0;
-    border: 1px solid var(--insertr-border-color);
-    border-radius: var(--insertr-border-radius);
-    cursor: pointer;
-    transition: var(--insertr-transition);
-    background: var(--insertr-bg-primary);
-    color: var(--insertr-text-primary);
-}
-
-.insertr-version-item:hover {
-    background: var(--insertr-bg-secondary);
-}
-
-.insertr-version-item.selected {
-    border-color: var(--insertr-primary);
-    background: rgba(0, 123, 255, 0.1);
-}
-
-.insertr-version-date {
-    font-weight: 500;
-    color: var(--insertr-text-primary);
-    margin: 0;
-    padding: 0;
-}
-
-.insertr-version-preview {
-    margin: var(--insertr-spacing-xs) 0 0 0;
-    padding: 0;
-    font-size: var(--insertr-font-size-sm);
-    color: var(--insertr-text-secondary);
-    white-space: pre-wrap;
-    word-break: break-word;
-}
-
-.insertr-version-actions {
-    display: flex;
-    gap: var(--insertr-spacing-sm);
-    justify-content: flex-end;
-    margin: 0;
-    padding: var(--insertr-spacing-md) 0 0 0;
-    border-top: 1px solid var(--insertr-border-color);
-}
-
-.insertr-btn-restore,
-.insertr-btn-close {
-    background: var(--insertr-primary);
-    color: var(--insertr-text-inverse);
-    border: none;
-    border-radius: var(--insertr-border-radius);
-    padding: var(--insertr-spacing-sm) var(--insertr-spacing-md);
-    margin: 0;
-    font-family: var(--insertr-font-family);
-    font-size: var(--insertr-font-size-base);
-    font-weight: 500;
-    cursor: pointer;
-    transition: var(--insertr-transition);
-    line-height: var(--insertr-line-height);
-    text-decoration: none;
-    display: inline-block;
-    text-align: center;
-    vertical-align: middle;
-}
-
-.insertr-btn-close {
-    background: var(--insertr-text-secondary);
-    color: var(--insertr-text-inverse);
-}
-
-.insertr-btn-close:hover {
-    background: var(--insertr-text-primary);
-    color: var(--insertr-text-inverse);
-}
-
-.insertr-btn-restore:hover {
-    background: var(--insertr-primary-hover);
-    color: var(--insertr-text-inverse);
-}
-
-.insertr-btn-restore:focus,
-.insertr-btn-close:focus {
-    outline: 2px solid var(--insertr-primary);
-    outline-offset: 2px;
-}
 
 /* =================================================================
    STATUS AND FEEDBACK MESSAGES