feat(mac): add agent-controlled Canvas panel

apps/macos/Sources/Clawdis/CanvasScheme.swift

@@ -0,0 +1,40 @@
+import Foundation
+
+enum CanvasScheme {
+    static let scheme = "clawdis-canvas"
+
+    static func makeURL(session: String, path: String? = nil) -> URL? {
+        var comps = URLComponents()
+        comps.scheme = Self.scheme
+        comps.host = session
+        let p = (path ?? "/").trimmingCharacters(in: .whitespacesAndNewlines)
+        if p.isEmpty || p == "/" {
+            comps.path = "/"
+        } else if p.hasPrefix("/") {
+            comps.path = p
+        } else {
+            comps.path = "/" + p
+        }
+        return comps.url
+    }
+
+    static func mimeType(forExtension ext: String) -> String {
+        switch ext.lowercased() {
+        case "html", "htm": "text/html; charset=utf-8"
+        case "js", "mjs": "application/javascript; charset=utf-8"
+        case "css": "text/css; charset=utf-8"
+        case "json", "map": "application/json; charset=utf-8"
+        case "svg": "image/svg+xml"
+        case "png": "image/png"
+        case "jpg", "jpeg": "image/jpeg"
+        case "gif": "image/gif"
+        case "ico": "image/x-icon"
+        case "woff2": "font/woff2"
+        case "woff": "font/woff"
+        case "ttf": "font/ttf"
+        case "wasm": "application/wasm"
+        default: "application/octet-stream"
+        }
+    }
+}
+