fix(cli): never print "[object Object]" from validate/inspect errors (#1810)

* fix(cli): use normalizeErrorMessage so validate/inspect never print "[object Object]"

The validate and inspect (layout) commands formatted thrown values with
`err instanceof Error ? err.message : String(err)`. When a browser/CDP/
Puppeteer protocol error or a structured page error reaches the formatter
as a plain object without a string `message`, `String(obj)` yields the
useless literal "[object Object]", hiding the real cause.

Route those paths through the existing shared `normalizeErrorMessage`
helper, which returns an Error's message, a string as-is, an object's
`.message` when present, or a compact JSON serialization otherwise (with
a key-list and String fallback for circular/opaque objects). Also fold
the duplicated local `errorMessage` helpers in batchRender and preview
into the same shared helper.

Covered by added assertions in errorMessage.test.ts for the no-message
object and Puppeteer-style protocol-error object cases.

* fix(cli): route remaining browser/process error sites through normalizeErrorMessage

The validate/inspect fix routed only those two commands through the shared
normalizeErrorMessage helper. The same err instanceof Error ? err.message :
String(err) pattern survived in the other commands that drive a headless
browser or an external process (ffmpeg, Docker, CDP) or surface a network
API error, so a thrown structured object without a string message would
still render as the useless literal [object Object].

Route those sites through the shared helper:
  snapshot.ts (the closest sibling to validate/inspect, same bug class),
  render.ts (Chrome launch + Docker build), capture/index.ts and
  commands/capture.ts (page-driven extraction), auth/browser.ts,
  browser/manager.ts (Puppeteer browser resolution), and the cloud/lambda
  paths (cloud/render.ts, cloudrun.ts, lambda/render-batch.ts,
  lambda/policies.ts, cloud/detectAspectRatio.ts) that surface API/network
  error objects.

Only the message-deriving expression changes; control flow and error
propagation are untouched. capture/index.ts keeps appending the stack for
real Errors and only routes the non-Error branch. Adds a helper test for a
structured CDP-style error object (code + nested data, no message).

packages/cli/src/commands/snapshot.ts

@@ -5,6 +5,7 @@ import { existsSync, mkdtempSync, readFileSync, mkdirSync, rmSync, writeFileSync
 import { tmpdir } from "node:os";
 import { resolve, join, relative, isAbsolute, basename } from "node:path";
 import { resolveProject } from "../utils/project.js";
+import { normalizeErrorMessage } from "../utils/errorMessage.js";
 import { resolveCompositionViewportFromHtml } from "../utils/compositionViewport.js";
 import { serveStaticProjectHtml } from "../utils/staticProjectServer.js";
 import { c } from "../ui/colors.js";
@@ -594,8 +595,7 @@ export default defineCommand({
                 descriptions.push(`## ${result.value.filename}`, `${result.value.desc}`, ``);
               } else {
                 // Log first failure so Gemini issues are visible rather than silent
-                const errMsg =
-                  result.reason instanceof Error ? result.reason.message : String(result.reason);
+                const errMsg = normalizeErrorMessage(result.reason);
                 descriptions.push(`## (error)`, `Gemini call failed: ${errMsg.slice(0, 120)}`, ``);
               }
             }
@@ -605,12 +605,12 @@ export default defineCommand({
             console.log(`   ${c.dim("descriptions.md")} (Gemini frame analysis)`);
           }
         } catch (descErr) {
-          const msg = descErr instanceof Error ? descErr.message : String(descErr);
+          const msg = normalizeErrorMessage(descErr);
           console.log(`   ${c.dim(`--describe failed: ${msg.slice(0, 80)}`)}`);
         }
       }
     } catch (err) {
-      const msg = err instanceof Error ? err.message : String(err);
+      const msg = normalizeErrorMessage(err);
       console.error(`\n${c.error("✗")} Snapshot failed: ${msg}`);
       process.exit(1);
     }