feat: complete code cleanup and create feature parity plan

Major Architecture Improvements:
- Separate JavaScript library (lib/) with proper build system
- Go CLI with embedded library using go:embed
- Hot reload development with Air integration
- Library + CLI build pipeline with npm run build

Code Cleanup:
- Remove obsolete assets (insertr-cli/assets/editor/)
- Clean up package.json metadata and dependencies
- Update .gitignore for new architecture
- Remove unused 'marked' dependency

New Documentation:
- Add comprehensive TODO.md with feature gap analysis
- Document critical gaps between prototype and current library
- Create phased implementation plan for feature parity
- Update DEVELOPMENT.md with hot reload workflow
- Add LIBRARY.md documenting new architecture

Hot Reload System:
- Air watches both Go CLI and JavaScript library
- Library changes trigger: rebuild → copy → CLI rebuild → serve
- Seamless development experience across full stack

Next Steps:
- Current library is basic proof-of-concept (prompt() editing)
- Archived prototype has production-ready features
- Phase 1 focuses on professional forms and authentication
- Phase 2 adds validation and content persistence

lib/src/core/insertr.js

@@ -0,0 +1,32 @@
+/**
+ * InsertrCore - Core functionality for content management
+ */
+export class InsertrCore {
+    constructor(options = {}) {
+        this.options = {
+            apiEndpoint: options.apiEndpoint || '/api/content',
+            siteId: options.siteId || 'default',
+            ...options
+        };
+    }
+    
+    // Find all enhanced elements on the page
+    findEnhancedElements() {
+        return document.querySelectorAll('[data-insertr-enhanced="true"]');
+    }
+    
+    // Get element metadata
+    getElementMetadata(element) {
+        return {
+            contentId: element.getAttribute('data-content-id'),
+            contentType: element.getAttribute('data-content-type'),
+            element: element
+        };
+    }
+    
+    // Get all elements with their metadata
+    getAllElements() {
+        const elements = this.findEnhancedElements();
+        return Array.from(elements).map(el => this.getElementMetadata(el));
+    }
+}