feat: split data update from site build; publish via Cloudflare Pages

The updater fetched GitHub metadata and rendered the dashboard payload in
a single step, so anything that published the site needed a GITHUB_TOKEN.
Cloudflare Pages builds from a Git webhook and has no business holding
one.

Split the tool into three modes. The default update step still fetches
GitHub and now records every API-sourced field in data/metadata.json,
which is committed alongside README.md and data/history.jsonl. The new
-build mode joins that snapshot with data/agents.yml and
data/history.jsonl to render dist/ with no network access and no token;
-check is unchanged.

Supporting changes:

- computeDeltaAt anchors the delta windows to when the data was fetched
  rather than the wall clock, so a redeploy days later reproduces the
  same Δ7d instead of sliding the window past its slack allowance.
- writeSiteData takes updatedAt explicitly for the same reason: the
  timestamp labels data freshness, not build time.
- sortStats is extracted from fetchStats so the build step re-ranks
  identically from committed metadata.
- An agents.yml entry with no metadata yet is omitted with a warning
  instead of failing the build, which would otherwise block every deploy
  between merging a new entry and the next nightly run.
- update.yml drops the GitHub Pages deploy steps and commits
  data/metadata.json; ci.yml runs `go run . -build` so a build that would
  break on deploy breaks in CI first.
- site/_headers stops the edge serving a stale data.json after a refresh.
- docs/DEPLOY.md covers the Cloudflare setup, including the one-time
  bootstrap of data/metadata.json that the build depends on.

Also carries the in-progress curation work already in the tree: the
module rename to awesome-ai-dev-tools, retagged entries, and removal of
the archived Roo-Code, void, continue and suna entries.

history.go

@@ -195,8 +195,16 @@ func computeDeltas(history []Snapshot, current Snapshot) map[string]int {
 // the delta would be misleadingly labeled "Δ<days>d", so we return no delta
 // for that repo instead.
 func computeDeltaOver(history []Snapshot, current Snapshot, days, slackDays int) map[string]int {
+	return computeDeltaAt(history, current, timeNow(), days, slackDays)
+}
+
+// computeDeltaAt is computeDeltaOver with an explicit anchor instead of the
+// wall clock. The build step passes the time the data was fetched, so
+// rebuilding an unchanged dataset later reproduces identical deltas rather
+// than sliding the window forward off its baseline.
+func computeDeltaAt(history []Snapshot, current Snapshot, anchor time.Time, days, slackDays int) map[string]int {
 	deltas := map[string]int{}
-	now := timeNow().UTC()
+	now := anchor.UTC()
 	cutoff := now.AddDate(0, 0, -days).Format("2006-01-02")
 	lowerBound := now.AddDate(0, 0, -(days + slackDays)).Format("2006-01-02")