perf(startup): load canvas, node-pty, ssh2, html-to-text and the OpenCode SDK on first use

Main module evaluation drops from ~420 ms to ~330 ms. Types stay as import type; the DeepSeek Harness chunks stay static because the protocol chunk shares code with Main startup paths.

src/main/lazy-require.ts

@@ -0,0 +1,14 @@
+import { createRequire } from 'node:module'
+
+/**
+ * Synchronously loads a dependency on first use instead of at module
+ * evaluation (P6). Main is ESM, but some test fixtures bundle the same code as
+ * CommonJS, where `import.meta.url` is empty and `__filename` exists instead.
+ */
+export function createLazyRequire<T>(specifier: string): () => T {
+  let loaded: T | undefined
+  return () => {
+    loaded ??= createRequire(import.meta.url || __filename)(specifier) as T
+    return loaded
+  }
+}