fix(ultrawork): lazy-load bun:sqlite to support Node/Electron runtime

Top-level `import { Database } from 'bun:sqlite'` caused Node/Electron's
ESM loader to reject the plugin at module-graph resolution time because
the `bun:` protocol is not in Node's allowed scheme list. This prevented
the OpenCode desktop app from loading the plugin at all.

Fix:
- Remove top-level static import of `bun:sqlite`
- Use a lazy importer (`_bunSqliteImporter`) that calls
  `import('bun:sqlite').catch(() => null)` at runtime
- If the import returns null (non-Bun environment), log a warning and
  return early — no DB override attempted, plugin loads normally
- Expose `__setBunSqliteImporterForTesting` / `__resetBunSqliteImporterForTesting`
  test seams to verify the Node/Electron fallback path

Closes #3795

src/plugin/ultrawork-db-model-override.bun-sqlite-unavailable.test.ts

@@ -0,0 +1,60 @@
+import { afterEach, beforeEach, describe, expect, mock, spyOn, test } from "bun:test"
+import * as sharedModule from "../shared"
+import {
+  scheduleDeferredModelOverride,
+  __setBunSqliteImporterForTesting,
+  __resetBunSqliteImporterForTesting,
+} from "./ultrawork-db-model-override"
+
+function flushMicrotasks(depth: number): Promise<void> {
+  return new Promise<void>((resolve) => {
+    let remaining = depth
+    function step() {
+      if (remaining <= 0) {
+        resolve()
+        return
+      }
+      remaining--
+      queueMicrotask(step)
+    }
+    queueMicrotask(step)
+  })
+}
+
+describe("scheduleDeferredModelOverride bun:sqlite unavailable", () => {
+  let logCalls: Array<[string, Record<string, unknown>?]> = []
+
+  beforeEach(() => {
+    // Simulate non-Bun runtime (Node/Electron): bun:sqlite import returns null
+    __setBunSqliteImporterForTesting(async () => null)
+
+    spyOn(sharedModule, "log").mockImplementation((message: string, metadata?: Record<string, unknown>) => {
+      logCalls.push([message, metadata])
+    })
+  })
+
+  afterEach(() => {
+    __resetBunSqliteImporterForTesting()
+    mock.restore()
+    logCalls = []
+  })
+
+  test("#given non-Bun runtime #when scheduleDeferredModelOverride is called #then it returns without throwing", async () => {
+    //#given
+    //#when
+    expect(() => {
+      scheduleDeferredModelOverride("msg_unavailable", {
+        providerID: "anthropic",
+        modelID: "claude-opus-4-7",
+      })
+    }).not.toThrow()
+
+    await flushMicrotasks(5)
+
+    //#then
+    const logMessages = logCalls.map(([msg]) => msg)
+    expect(logMessages).toContain(
+      "[ultrawork-db-override] bun:sqlite unavailable (non-Bun runtime), skipping deferred override",
+    )
+  })
+})