Vendor frontend JS into javascript/; drop the prestartup copy dance

The viewer JS/HTML/bundles are now committed in javascript/ (declared via
pyproject [tool.comfy] web = "javascript") instead of being copied from the
shared comfy-3d-viewers pip package at prestartup. Consequences:

- requirements.txt is now just comfy-env (host env installs nothing else,
  per the never-touch-the-host-env principle)
- prestartup_script.py no longer copies viewers or web_src; it keeps only
  setup_env() and the input-asset copies
- WEB_DIRECTORY attribute removed; the pyproject declaration is the single
  source (served at /extensions/comfyui-geometrypack/, keyed by project name)
- web_src/ deleted; its 6 widgets now live in javascript/js/ as the tracked
  source, edited directly
- viewer_pbr.html hardcoded-fallback URL updated to the new mount name

Iframe URLs auto-detect the mount from import.meta.url, so the folder rename
and mount-name change are transparent at runtime.

javascript/js/utils/postMessage.js

@@ -0,0 +1,196 @@
+/**
+ * PostMessage utilities for iframe communication
+ */
+
+/**
+ * Create a message sender function for an iframe
+ * @param {HTMLIFrameElement} iframe - The iframe element
+ * @param {string} logPrefix - Logging prefix (e.g., "[GeomPack VTK]")
+ * @returns {Function} Message sending function
+ */
+export function createMessageSender(iframe, logPrefix = "[Viewer]") {
+    return (data) => {
+        if (iframe.contentWindow) {
+            iframe.contentWindow.postMessage(data, "*");
+        } else {
+            console.error(`${logPrefix} Iframe contentWindow not available`);
+        }
+    };
+}
+
+/**
+ * Create a mesh load message
+ * @param {string} filepath - URL path to the mesh file
+ * @returns {Object} Message data object
+ */
+export function createLoadMeshMessage(filepath) {
+    return {
+        type: "LOAD_MESH",
+        filepath: filepath,
+        timestamp: Date.now()
+    };
+}
+
+/**
+ * Create a dual mesh load message
+ * @param {Object} options - Message options
+ * @returns {Object} Message data object
+ */
+export function createLoadDualMeshMessage(options) {
+    const {
+        layout,
+        mesh1Filepath,
+        mesh2Filepath,
+        meshFilepath,  // For overlay mode
+        opacity1 = 1.0,
+        opacity2 = 1.0,
+        showEdges = false,
+        cameraState = "",
+        selectedField = "",
+        selectedChannel = "magnitude",
+        selectedColormap = "erdc_rainbow_bright",
+    } = options;
+
+    return {
+        type: 'LOAD_DUAL_MESH',
+        layout: layout,
+        mesh1Filepath,
+        mesh2Filepath,
+        meshFilepath,
+        opacity1,
+        opacity2,
+        showEdges,
+        cameraState,
+        selectedField,
+        selectedChannel,
+        selectedColormap,
+        timestamp: Date.now()
+    };
+}
+
+/**
+ * Build ComfyUI view API URL for a file.
+ * Handles absolute paths (/home/.../output/sub/file.glb),
+ * relative paths (output/sub/file.glb), and bare filenames (file.glb).
+ * @param {string} filename - The filename or path
+ * @param {string} defaultType - Default file type (default: "output")
+ * @param {string} defaultSubfolder - Default subfolder path (default: "")
+ * @returns {string} API URL
+ */
+export function buildViewUrl(filename, defaultType = "output", defaultSubfolder = "") {
+    const normalized = filename.replace(/\\/g, '/');
+    const pathMatch = normalized.match(/(?:^|\/)(output|input|temp)\/(.+)$/);
+    if (pathMatch) {
+        const [, type, relPath] = pathMatch;
+        const parts = relPath.split('/');
+        const fname = parts.pop();
+        const subfolder = parts.join('/');
+        return `/view?filename=${encodeURIComponent(fname)}&type=${type}&subfolder=${encodeURIComponent(subfolder)}`;
+    }
+    // Bare filename fallback
+    const basename = normalized.split('/').pop();
+    return `/view?filename=${encodeURIComponent(basename)}&type=${defaultType}&subfolder=${defaultSubfolder}`;
+}
+
+/**
+ * Create an iframe viewer manager for handling viewer switching
+ * @param {HTMLIFrameElement} iframe - The iframe element
+ * @param {string} logPrefix - Logging prefix
+ * @returns {Object} Viewer manager object
+ */
+export function createViewerManager(iframe, logPrefix = "[Viewer]") {
+    let currentViewerType = null;
+    let iframeLoaded = false;
+    let pendingMessage = null;
+
+    // Track iframe load state
+    iframe.addEventListener('load', () => {
+        iframeLoaded = true;
+        // Send pending message if any
+        if (pendingMessage && iframe.contentWindow) {
+            iframe.contentWindow.postMessage(pendingMessage, "*");
+            pendingMessage = null;
+        }
+    });
+
+    return {
+        /**
+         * Get current viewer type
+         * @returns {string|null}
+         */
+        getCurrentType() {
+            return currentViewerType;
+        },
+
+        /**
+         * Check if iframe is loaded
+         * @returns {boolean}
+         */
+        isLoaded() {
+            return iframeLoaded;
+        },
+
+        /**
+         * Send a message to the iframe viewer
+         * If iframe is not loaded yet, queue the message
+         * @param {Object} data - Message data
+         */
+        sendMessage(data) {
+            if (iframeLoaded && iframe.contentWindow) {
+                iframe.contentWindow.postMessage(data, "*");
+            } else {
+                pendingMessage = data;
+            }
+        },
+
+        /**
+         * Switch to a different viewer type if needed
+         * @param {string} viewerType - New viewer type
+         * @param {string} viewerUrl - URL of the new viewer
+         * @param {Object} messageData - Message to send after viewer loads
+         * @returns {boolean} True if viewer was switched, false if already on correct viewer
+         */
+        switchViewer(viewerType, viewerUrl, messageData) {
+            if (viewerType === currentViewerType) {
+                // No switch needed, just send message
+                this.sendMessage(messageData);
+                return false;
+            }
+
+            // Viewer switch needed
+            currentViewerType = viewerType;
+            iframeLoaded = false;
+            pendingMessage = messageData;
+
+            // Change iframe src to trigger reload
+            iframe.src = viewerUrl + "?v=" + Date.now();
+            return true;
+        },
+
+        /**
+         * Reset the manager state
+         */
+        reset() {
+            currentViewerType = null;
+            iframeLoaded = false;
+            pendingMessage = null;
+        }
+    };
+}
+
+/**
+ * Create an error message handler for iframe errors
+ * @param {HTMLElement} infoPanel - The info panel to display errors
+ * @param {string} logPrefix - Logging prefix
+ * @returns {Function} Event handler function
+ */
+export function createErrorHandler(infoPanel, logPrefix = "[Viewer]") {
+    return (event) => {
+        if (event.data.type === 'MESH_ERROR' && event.data.error) {
+            console.error(`${logPrefix} Error from viewer:`, event.data.error);
+            if (infoPanel) {
+                infoPanel.innerHTML = `<div style="color: #ff6b6b; padding: 8px;">Error: ${event.data.error}</div>`;
+            }
+        }
+    };
+}