chore(deps): sweep Dependabot alerts into board-tracked issues

Closes #2233 — the alert-consuming half of #2229. #2235 removed
`.github/dependabot.yml`, ending Dependabot's version-update PRs; this
ends its security-update PRs and replaces them with a daily sweep that
turns the alerts into ordinary board items.

- `scripts/dependabot-alerts.mjs` groups alerts by
  `(package, manifest_path, first_patched_version)` — one issue per
  BUMP, not per advisory — re-checks each vulnerable range against
  `v2/main`'s own lockfile before filing, and keys idempotency on a
  marker comment naming every GHSA the issue covers.
- `.github/workflows/dependabot-alerts.yml` runs it daily and on
  `workflow_dispatch`, with `vulnerability-alerts: read`.
- `semver` is declared at the repo root, per Dependency placement:
  `scripts/` is root-owned code with no manifest of its own.
- The sibling `dependency-refresh` comments no longer claim security
  updates are unaffected, and AGENTS.md gains the flow both halves
  now follow.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013H6Cew3KB3jVmQ5x4Dq1sq
Signed-off-by: cliffhall <cliff@futurescale.com>

scripts/dependency-refresh.mjs

@@ -3,12 +3,13 @@
 //
 // A Dependabot version-update PR carries no issue and no board card — the same
 // carve-out from "every PR references an issue" that the security-update flow
-// had (that half is handled separately by the alert-driven pipeline, also
-// #2229). #2235 removed `.github/dependabot.yml` outright, so Dependabot opens
+// had (that half is `dependabot-alerts.mjs`, #2233, which turned those PRs off
+// as well and files an issue per bump from the alerts they leave behind — so
+// between them Dependabot opens no PRs against this repo at all, though its
+// security ALERTS stay on, since that sweep is what consumes them).
+// #2235 removed `.github/dependabot.yml` outright, so Dependabot opens
 // no version-update PRs against this repo at all and this script is what
-// replaced them. Dependabot SECURITY updates are a separate mechanism, enabled
-// in repo settings rather than in that file, and are deliberately still on —
-// so this replaces the version-update half only, not Dependabot wholesale.
+// replaced them.
 //
 // Once a month it runs `npm outdated` across the root install and every client
 // under `clients/*` (each has its own package.json + lockfile — v2 is not a