feat: Phase 1 — extract the client (web SPA + desktop) to dtoro/oikos-web

Problem: the hexagonal refactor churns the backend tree for nine more
phases; the UI delivery stack (web/ SPA, cmd/desktop Wails wrapper,
compose/web image) must move to its own repo first so doc/layout
rewrites land once on a backend-only tree.

Change:
- New repo git.hubris.network/dtoro/oikos-web (v0.33.0): web/, desktop/
  (updateURL repointed to oikos-web releases), compose/, own CI (web +
  desktop jobs), own deploy script (CI-green gate, TOCTOU guard,
  version-tagged images, prune-to-3), own webhook receiver on :9798 +
  launchd unit, own compose project publishing the same 8091:80.
- Cutover executed on mac-mini in order: oikos stack's web service
  stopped+removed, oikos-web project brought up on 8091; outer Caddy
  untouched (targets the published port) — serving + Authentik flow +
  /wails 404 quirk verified post-cutover.
- Stripped from oikos: web/, cmd/desktop/, compose/web/, desktop CI
  workflow, ci.yml web job, Makefile ui/desktop/desktop-package/install
  targets, the compose web service, oikos-web from deploy.sh's fallback
  prune list; wails + go-keyring dropped from go.mod, vendor synced.
- README / CONTRIBUTING / AGENTS.md / .agents dev+operations docs now
  point at the new repo; mbse + mascot design docs carry a path note.

Risk: production SPA serving depends on the new pipeline now; rollback
is versioned-image re-up of the old web service from a pre-split
checkout (port 8091). Desktop builds installed before the split still
check dtoro/oikos releases — one manual reinstall, noted in the
oikos-web release notes.

Verification: go vet, make test (race), make generate-check, golangci
(no new findings; baseline down 400→365); post-cutover curls —
localhost:8091 200, /wails/runtime.js 404, outer Caddy 302 Authentik.

web/node_modules/stackback/index.js

@@ -0,0 +1,46 @@
+
+// v8 builtin format stack trace
+// for when there was no previous prepareStackTrace function to call
+var FormatStackTrace = require('./formatstack');
+
+// some notes on the behavior below:
+// because the 'stack' member is a one shot access variable (the raw stack is
+// formatted on accessing it)
+// we try to avoid modifying what the user would have wanted
+// thus we use the previous value for prepareStackTrace
+//
+// The reason we store the callsite variable is because prepareStackTrace
+// will not be called again once it has been called for a given error object
+// but we want to support getting the stack out of the error multiple times (cause why not)
+module.exports = function(err) {
+
+    // save original stacktrace
+    var save = Error.prepareStackTrace;
+
+    // replace capture with our function
+    Error.prepareStackTrace =  function(err, trace) {
+
+        // cache stack frames so we don't have to get them again
+        // use a non-enumerable property
+        Object.defineProperty(err, '_sb_callsites', {
+            value: trace
+        });
+
+        return (save || FormatStackTrace)(err, trace);
+    };
+
+    // force capture of the stack frames
+    err.stack;
+
+    // someone already asked for the stack so we can't do this trick
+    // TODO fallback to string parsing?
+    if (!err._sb_callsites) {
+        return [];
+    }
+
+    // return original capture function
+    Error.prepareStackTrace = save;
+
+    return err._sb_callsites;
+};
+