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.test.ts

@@ -0,0 +1,24 @@
+// @vitest-environment node
+import { describe, expect, it } from 'vitest'
+import { createLazyRequire } from './lazy-require'
+import { loadHtmlToText } from './document-extracted-text'
+import { loadSsh2 } from './ssh/ssh2-module'
+
+describe('createLazyRequire', () => {
+  it('loads a module on first call and returns the cached instance afterwards', () => {
+    const load = createLazyRequire<typeof import('node:path')>('node:path')
+    const first = load()
+    expect(typeof first.join).toBe('function')
+    expect(load()).toBe(first)
+  })
+
+  it('surfaces a missing module at first use, not at import time', () => {
+    const load = createLazyRequire('goodbuddy-module-that-does-not-exist')
+    expect(load).toThrow()
+  })
+
+  it('resolves the deferred Main dependencies', () => {
+    expect(typeof loadHtmlToText().convert).toBe('function')
+    expect(typeof loadSsh2().Client).toBe('function')
+  })
+})