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/enhanced-resolve/lib/DirectoryExistsPlugin.js

@@ -0,0 +1,68 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+
+"use strict";
+
+/** @typedef {import("./Resolver")} Resolver */
+/** @typedef {import("./Resolver").ResolveStepHook} ResolveStepHook */
+
+module.exports = class DirectoryExistsPlugin {
+	/**
+	 * @param {string | ResolveStepHook} source source
+	 * @param {string | ResolveStepHook} target target
+	 */
+	constructor(source, target) {
+		this.source = source;
+		this.target = target;
+	}
+
+	/**
+	 * @param {Resolver} resolver the resolver
+	 * @returns {void}
+	 */
+	apply(resolver) {
+		const target = resolver.ensureHook(this.target);
+		resolver
+			.getHook(this.source)
+			.tapAsync(
+				"DirectoryExistsPlugin",
+				(request, resolveContext, callback) => {
+					const fs = resolver.fileSystem;
+					const directory = request.path;
+					if (!directory) return callback();
+					fs.stat(directory, (err, stat) => {
+						// Combine the two miss branches: a stat failure and a
+						// "not a directory" result share the same handling — record
+						// the path on `missingDependencies`, log the right reason,
+						// then bail. The error-message ternary picks the wording
+						// that matched the failing condition.
+						if (err || !stat || !stat.isDirectory()) {
+							if (resolveContext.missingDependencies) {
+								resolveContext.missingDependencies.add(directory);
+							}
+							if (resolveContext.log) {
+								resolveContext.log(
+									err || !stat
+										? `${directory} doesn't exist`
+										: `${directory} is not a directory`,
+								);
+							}
+							return callback();
+						}
+						if (resolveContext.fileDependencies) {
+							resolveContext.fileDependencies.add(directory);
+						}
+						resolver.doResolve(
+							target,
+							request,
+							`existing directory ${directory}`,
+							resolveContext,
+							callback,
+						);
+					});
+				},
+			);
+	}
+};