feat(web): split SPA from oikos binary, require auth on every route

Phase 0 of plans/2026-07-12-wails-desktop-app.md. The control-room SPA
is no longer embedded (web/embed.go deleted); it's a standalone static
build served separately (make ui / make deploy-ui). The api process
adds CORS and drops the dev-open auth bypass — every route now needs a
real bearer token, including SSE (?token= query param, EventSource
can't set headers) and api's own /agent proxy to nomos (previously
unauthenticated by omission).

nomos was an unauthenticated client of api's /mcp and approval-decision
endpoints; closing dev-open would have broken it, so it now sends
Authorization: Bearer $OIKOS_MCP_BEARER_TOKEN on every call back to api.

SPA gets a runtime config module (config.ts) and a Config.svelte
first-launch/reconfigure page, reachable afterwards via a "Connection"
entry in the sidebar footer. Every fetch() in api.ts routes through
fetchWithAuth so the same build works same-origin (browser prod, Vite
dev proxy) or cross-origin (future Wails webview, remote access).

Six gaps found against the plan and the live Caddy topology while
implementing — documented in the plan's "Plan review" section, most
notably: api's own /agent mount was never behind combinedAuth (fixed),
and production's Authentik forward-auth needs a bearer-token bypass for
API routes that this repo's Caddyfile.oikos reference copy now has, but
the real dtoro/caddy-conf deploy does not yet.

Verified live: cross-origin static SPA + API, CORS, bearer auth, SSE
query-token auth, and localStorage persistence all confirmed working
in-browser. Full Go test suite and npm run build pass with no
regressions against the pre-change baseline.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

internal/httpapi/mutations_test.go

@@ -24,9 +24,7 @@ func do(t *testing.T, h http.Handler, method, path string, body any, headers map
 	}
 	req := httptest.NewRequest(method, path, rdr)
 	req.Header.Set("Content-Type", "application/json")
-	for k, v := range headers {
-		req.Header.Set(k, v)
-	}
+	applyHeaders(req, headers)
 	rec := httptest.NewRecorder()
 	h.ServeHTTP(rec, req)
 	var decoded map[string]any