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/mode.js

@@ -0,0 +1,41 @@
+module.exports = isexe
+isexe.sync = sync
+
+var fs = require('fs')
+
+function isexe (path, options, cb) {
+  fs.stat(path, function (er, stat) {
+    cb(er, er ? false : checkStat(stat, options))
+  })
+}
+
+function sync (path, options) {
+  return checkStat(fs.statSync(path), options)
+}
+
+function checkStat (stat, options) {
+  return stat.isFile() && checkMode(stat, options)
+}
+
+function checkMode (stat, options) {
+  var mod = stat.mode
+  var uid = stat.uid
+  var gid = stat.gid
+
+  var myUid = options.uid !== undefined ?
+    options.uid : process.getuid && process.getuid()
+  var myGid = options.gid !== undefined ?
+    options.gid : process.getgid && process.getgid()
+
+  var u = parseInt('100', 8)
+  var g = parseInt('010', 8)
+  var o = parseInt('001', 8)
+  var ug = u | g
+
+  var ret = (mod & o) ||
+    (mod & g) && gid === myGid ||
+    (mod & u) && uid === myUid ||
+    (mod & ug) && myUid === 0
+
+  return ret
+}