Address review: MCPB build, guard the SDK's own handlers, doc fixes

- pdf-server build-mcpb.mjs packs the ext-apps build from this checkout
  into the staging dir instead of asking the registry for ^2.0.0, which
  is not published yet; CI's "Build MCPB bundle" step failed on ETARGET.
- Claim notifications/cancelled and notifications/progress in the
  MethodRegistry right after super() so a direct setNotificationHandler
  cannot silently replace the base Protocol's own handlers.
- Migration guide and add-app-to-server skill: custom methods use the
  three-argument setRequestHandler("m", { params }, handler) form (the
  two-argument form is only for spec methods); zod schemas live in
  @modelcontextprotocol/core, not client/server; it is
  toolInfo.tool.outputSchema that loosened in schema.json, and the
  recursive JSON-value def is nested under three definitions; core is a
  required peer that client already depends on.
- app-bridge.ts: fix "forthe"/"forresult" typos in @see links, update
  three JSDoc examples to the method-string setNotificationHandler form,
  move the UntypedHandlerSetter type below the import block (same in
  app.ts).
- wire-compat.test.ts: say the fixtures are 1.x-shaped, not captures.

examples/pdf-server/build-mcpb.mjs

@@ -43,6 +43,21 @@ writeFileSync(
   path.join(stage, "manifest.json"),
   JSON.stringify(manifest, null, 2),
 );
+// The bundle must ship the ext-apps build from this checkout, not whatever
+// the registry has: pack the repo root and point the staged manifest at it.
+const repoRoot = path.resolve(here, "..", "..");
+const packed = JSON.parse(
+  execSync(
+    "npm pack --json --ignore-scripts --pack-destination " +
+      JSON.stringify(stage),
+    {
+      cwd: repoRoot,
+      encoding: "utf8",
+    },
+  ).replace(/^[^[]*/, ""),
+);
+pkg.dependencies["@modelcontextprotocol/ext-apps"] =
+  "file:./" + packed[0].filename;
 writeFileSync(path.join(stage, "package.json"), JSON.stringify(pkg, null, 2));
 
 const run = (cmd) => execSync(cmd, { cwd: stage, stdio: "inherit" });