feat: upgrade to upstream v2026.3.28

Major upgrade from e26988a38 to upstream v2026.3.28 (f9b107928).
Key changes:
- Upstream src/, ui/, extensions/ (89 bundled extensions)
- Zero-token web providers preserved in src/zero-token/
- AskOnce plugin restored and registered as CLI command
- Added missing packages: @anthropic-ai/vertex-sdk, @modelcontextprotocol/sdk
- Fixed tsconfig rootDir, skipLibCheck for plugin-sdk DTS build
- Added askonce to bundled plugin metadata and package.json exports
- Fixed AskOnce CLI command registration (missing commands metadata)
- Restored AskOnce adapter imports (correct 5-level relative paths)
- Removed stale migration artifacts from root directory

cli/program/program-context.test.ts

@@ -0,0 +1,38 @@
+import { Command } from "commander";
+import { describe, expect, it } from "vitest";
+import type { ProgramContext } from "./context.js";
+import { getProgramContext, setProgramContext } from "./program-context.js";
+
+function makeCtx(version: string): ProgramContext {
+  return {
+    programVersion: version,
+    channelOptions: ["telegram"],
+    messageChannelOptions: "telegram",
+    agentChannelOptions: "last|telegram",
+  };
+}
+
+describe("program context storage", () => {
+  it("stores and retrieves context on a command instance", () => {
+    const program = new Command();
+    const ctx = makeCtx("1.2.3");
+    setProgramContext(program, ctx);
+    expect(getProgramContext(program)).toBe(ctx);
+  });
+
+  it("returns undefined when no context was set", () => {
+    expect(getProgramContext(new Command())).toBeUndefined();
+  });
+
+  it("does not leak context between command instances", () => {
+    const programA = new Command();
+    const programB = new Command();
+    const ctxA = makeCtx("a");
+    const ctxB = makeCtx("b");
+    setProgramContext(programA, ctxA);
+    setProgramContext(programB, ctxB);
+
+    expect(getProgramContext(programA)).toBe(ctxA);
+    expect(getProgramContext(programB)).toBe(ctxB);
+  });
+});