feat(telemetry): Sentry + PostHog quality pass (#546)

Comprehensive telemetry quality improvements across Sentry and PostHog, grounded in an audit of the live data plus current best-practice research.

Sentry: job_id/instance_id tags, operational fingerprinting, PII-safe settings context on bug events, web tag population + extension-noise filtering, an early-crash buffer, http status/method kept on breadcrumbs, and a gated-off-by-default performance-tracing re-enable (tracesSampler that zeroes db/redis/queue-poll root spans + drops the Redis integration) with worker job spans and canonical-host cron monitors.

PostHog: history_change SPA pageviews, instance_id super property for fleet rollups, enriched tool_used (formats, byte sizes, is_batch, execution_hint, real error_kind taxonomy), the previously-dead result_saved/batch_processed/ai_bundle_prompted events fired, search click-through, editor + Automate authoring + auth instrumentation, a before_send PII boundary, and minimal opt-in landing-site pageviews.

tests/unit/web/early-errors.test.ts

@@ -0,0 +1,56 @@
+// @vitest-environment jsdom
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import {
+  flushEarlyErrors,
+  resetEarlyErrorsForTests,
+  startEarlyErrorCapture,
+} from "../../../apps/web/src/lib/early-errors.js";
+
+const h = vi.hoisted(() => ({ captureException: vi.fn(), client: {} as object | undefined }));
+vi.mock("@sentry/react", () => ({
+  captureException: h.captureException,
+  getClient: () => h.client,
+}));
+
+// Guard so jsdom does not surface these synthetic error events as "uncaught"
+// (production code intentionally never preventDefaults real errors).
+const guard = (e: Event) => e.preventDefault();
+beforeEach(() => {
+  resetEarlyErrorsForTests();
+  vi.clearAllMocks();
+  h.client = {};
+  window.addEventListener("error", guard);
+});
+afterEach(() => window.removeEventListener("error", guard));
+
+describe("early error buffer", () => {
+  it("buffers a pre-init error and replays it to Sentry on flush", async () => {
+    startEarlyErrorCapture();
+    const boom = new Error("early boom");
+    window.dispatchEvent(new ErrorEvent("error", { error: boom, cancelable: true }));
+
+    await flushEarlyErrors();
+
+    expect(h.captureException).toHaveBeenCalledTimes(1);
+    expect(h.captureException).toHaveBeenCalledWith(boom);
+  });
+
+  it("does not replay when Sentry never initialized (opt-out safe)", async () => {
+    startEarlyErrorCapture();
+    window.dispatchEvent(new ErrorEvent("error", { error: new Error("x"), cancelable: true }));
+    h.client = undefined; // no Sentry client -> analytics off
+
+    await flushEarlyErrors();
+
+    expect(h.captureException).not.toHaveBeenCalled();
+  });
+
+  it("stops buffering after flush so post-init errors are left to the SDK", async () => {
+    startEarlyErrorCapture();
+    await flushEarlyErrors();
+    window.dispatchEvent(new ErrorEvent("error", { error: new Error("late"), cancelable: true }));
+    await flushEarlyErrors();
+
+    expect(h.captureException).not.toHaveBeenCalled();
+  });
+});