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/postcss/lib/postcss.mjs

@@ -0,0 +1,30 @@
+import postcss from './postcss.js'
+
+export default postcss
+
+export const stringify = postcss.stringify
+export const fromJSON = postcss.fromJSON
+export const plugin = postcss.plugin
+export const parse = postcss.parse
+export const list = postcss.list
+
+export const document = postcss.document
+export const comment = postcss.comment
+export const atRule = postcss.atRule
+export const rule = postcss.rule
+export const decl = postcss.decl
+export const root = postcss.root
+
+export const CssSyntaxError = postcss.CssSyntaxError
+export const Declaration = postcss.Declaration
+export const Container = postcss.Container
+export const Processor = postcss.Processor
+export const Document = postcss.Document
+export const Comment = postcss.Comment
+export const Warning = postcss.Warning
+export const AtRule = postcss.AtRule
+export const Result = postcss.Result
+export const Input = postcss.Input
+export const Rule = postcss.Rule
+export const Root = postcss.Root
+export const Node = postcss.Node