analytics: make each weekly funnel stage separately measurable (FRE-366)

Gap 1 — click and served share one label: trackDownload now takes a
stage ("click" | "served") carried on a new VisitorAnalytics.stage
column; the Nook door and the tRPC proxy record clicks, the DMG file
route records served. summariseDownloads() and the /analytics downloads
block are untouched — the stage is a separate column, so the path
grouping cannot change.

Gap 2 — checkout start records nothing: the checkout route records a
created Stripe session through the shared trackRequest writer (same
referrer, campaign, country dimensions as every door) under its own
path, and STAGES.checkout reads it instead of the /checkout page proxy.

Gap 3 — loopback addresses, no host dimension: every writer now
resolves the client address through resolveClientIp, which trusts
x-forwarded-for only when the direct peer is the loopback production
proxy (trust boundary stated in request-client.ts), and records the
host on each row through the same site-context extractor routing uses.
stage and host reach the table through VISITOR_ANALYTICS_ADDED_COLUMNS;
the weekly job applies the same bootstrap before reading so it renders
seven stages against a database no deploy has migrated yet.

The weekly read splits downloadClick/dmgServed, scopes visits to
nook.freno.me, and computes its caveats from the window: pre-instrumentation
rows are stated and excluded, and the loopback warning now fires only
when rows recorded since the instrumentation still carry it.

scripts/weekly-metrics.ts

@@ -2,6 +2,7 @@ import { createClient } from "@libsql/client/web";
 import { mkdir, writeFile } from "node:fs/promises";
 import { dirname, resolve } from "node:path";
 import {
+  ensureAnalyticsSchema,
   getWeeklyReport,
   renderWeeklyMarkdown,
   type Connections
@@ -123,6 +124,11 @@ async function main(): Promise<void> {
     nook: connect(requiredEnv("NOOK_DB_URL"), requiredEnv("NOOK_DB_TOKEN"))
   };
 
+  // The app migrates the table on boot, but this job must not depend on a
+  // deploy having happened: add any missing post-hoc columns (stage, host)
+  // through the same idempotent bootstrap path first.
+  await ensureAnalyticsSchema(connections.analytics);
+
   const report = await getWeeklyReport(connections, {
     days: options.days,
     now: options.now
@@ -141,8 +147,8 @@ async function main(): Promise<void> {
   console.log(
     `wrote ${options.out}\n` +
       `window ${report.window.start} → ${report.window.end}\n` +
-      `visit ${f.visit}, download ${f.download}, trial ${f.trial}, ` +
-      `checkout ${f.checkout}, purchase ${f.purchase}, activation ${f.activation}\n` +
+      `visit ${f.visit}, download click ${f.downloadClick}, DMG served ${f.dmgServed}, ` +
+      `trial ${f.trial}, checkout ${f.checkout}, purchase ${f.purchase}, activation ${f.activation}\n` +
       `mover: ${report.mover ? `${report.mover.label} ${report.mover.before} → ${report.mover.now}` : "none"}`
   );
 }