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/isexe/index.js

@@ -0,0 +1,57 @@
+var fs = require('fs')
+var core
+if (process.platform === 'win32' || global.TESTING_WINDOWS) {
+  core = require('./windows.js')
+} else {
+  core = require('./mode.js')
+}
+
+module.exports = isexe
+isexe.sync = sync
+
+function isexe (path, options, cb) {
+  if (typeof options === 'function') {
+    cb = options
+    options = {}
+  }
+
+  if (!cb) {
+    if (typeof Promise !== 'function') {
+      throw new TypeError('callback not provided')
+    }
+
+    return new Promise(function (resolve, reject) {
+      isexe(path, options || {}, function (er, is) {
+        if (er) {
+          reject(er)
+        } else {
+          resolve(is)
+        }
+      })
+    })
+  }
+
+  core(path, options || {}, function (er, is) {
+    // ignore EACCES because that just means we aren't allowed to run it
+    if (er) {
+      if (er.code === 'EACCES' || options && options.ignoreErrors) {
+        er = null
+        is = false
+      }
+    }
+    cb(er, is)
+  })
+}
+
+function sync (path, options) {
+  // my kingdom for a filtered catch
+  try {
+    return core.sync(path, options || {})
+  } catch (er) {
+    if (options && options.ignoreErrors || er.code === 'EACCES') {
+      return false
+    } else {
+      throw er
+    }
+  }
+}