docs: mark repo as archived (#19)

The app has been sunset and all cloud infrastructure torn down. Add a
prominent archived banner at the top of the README and a note in the
"Running it" section clarifying the steps are for exploring the archived
code offline, not redeploying.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: vicw0ng-hk

README.md

@@ -1,6 +1,16 @@
 # HK IPO Verify (hipo)
 
-**Live:** [hipo.vsh852.com](https://hipo.vsh852.com)
+> ## 🗄️ Archived (2026-07-22)
+>
+> **This project has been sunset.** The live site (`hipo.vsh852.com`) is offline
+> and all cloud infrastructure — the AWS Lambda agent backend, the Cloudflare
+> Pages SPA, the catalog Worker, and the R2/KV stores — has been torn down. The
+> repo is preserved read-only as a portfolio archive; the code, design docs, and
+> commit history remain intact and the `mise run check` gate still passes
+> offline. The `infra/*.tf` resource blocks and the `deploy-*` workflows are
+> commented out (not deleted) so the architecture stays readable — restore them
+> from git history to redeploy. See [docs/progress.md](docs/progress.md) for the
+> teardown record.
 
 Browse recent Hong Kong IPO filings — Application Proofs, PHIPs, and
 prospectuses — pick one, and watch a **bounded analysis agent** turn it into a
@@ -170,6 +180,10 @@ Deploy, secrets, bootstrap, and verification detail live in
 
 ## Running it
 
+> Archived: the deployed stack is gone, but the code still builds and the
+> `mise run check` gate still passes offline. The steps below are for exploring
+> the archived project locally, not for redeploying.
+
 ### Prerequisites
 
 - [`mise`](https://mise.jdx.dev) — task runner + non-Python tool versions