feat(settings): /settings/workspace — edit company info + invoice defaults

Owner/admin edit, member read-only.

Schema/validation:
- lib/validation/workspace.ts (workspaceSettingsSchema)
- lib/appwrite/workspace-actions.ts:
  * updateWorkspaceSettingsAction — requireRole owner|admin, upserts the
    tenant_settings row (creates one with team-scoped perms if absent,
    e.g. for tenants created before tenant_settings was a table; just
    defense). Audit-logged.
  * Forces invoicePrefix to uppercase. defaultVatRate clamped to [0, 100].
  * revalidatePath('/', 'layout') so the new company name updates in
    sidebar header and dashboard greeting on next render.

UI:
- /settings/workspace page (server) — pulls active tenant settings
  via requireTenant, shows form pre-filled.
- WorkspaceSettingsForm: 2 cards
  * Şirket — name (required), tax id, phone, email, address
  * Faturalama — invoicePrefix, defaultVatRate, read-only invoiceCounter
- All inputs disabled if user is a member (canEdit=false). Submit button
  hidden in that case. Description on the page changes accordingly.
- Toast feedback for success/error.

Skipped: logo upload (storage bucket pending). Will revisit.

src/app/(dashboard)/settings/workspace/page.tsx

@@ -0,0 +1,50 @@
+import type { Metadata } from "next";
+import { redirect } from "next/navigation";
+
+import { requireTenant } from "@/lib/appwrite/tenant-guard";
+import { WorkspaceSettingsForm } from "./components/workspace-form";
+
+export const metadata: Metadata = {
+  title: "İşletmem — Şirket bilgileri",
+};
+
+export default async function WorkspaceSettingsPage() {
+  let ctx;
+  try {
+    ctx = await requireTenant();
+  } catch {
+    redirect("/onboarding");
+  }
+
+  const canEdit = ctx.role === "owner" || ctx.role === "admin";
+
+  return (
+    <div className="flex-1 space-y-6 px-6 pt-0">
+      <div className="flex flex-col gap-1">
+        <p className="text-muted-foreground text-sm">{ctx.settings?.companyName ?? "Çalışma alanı"}</p>
+        <h1 className="text-2xl font-bold tracking-tight">Şirket bilgileri</h1>
+        <p className="text-muted-foreground text-sm">
+          Faturalarda ve panel başlığında görünecek şirket bilgileri.
+          {!canEdit && " Düzenlemek için yönetici yetkisine ihtiyacınız var."}
+        </p>
+      </div>
+
+      <WorkspaceSettingsForm
+        canEdit={canEdit}
+        defaults={{
+          companyName: ctx.settings?.companyName ?? "",
+          companyTaxId: ctx.settings?.companyTaxId ?? "",
+          companyAddress: ctx.settings?.companyAddress ?? "",
+          companyEmail: ctx.settings?.companyEmail ?? "",
+          companyPhone: ctx.settings?.companyPhone ?? "",
+          defaultVatRate:
+            typeof ctx.settings?.defaultVatRate === "number"
+              ? ctx.settings.defaultVatRate
+              : 20,
+          invoicePrefix: ctx.settings?.invoicePrefix ?? "INV",
+          invoiceCounter: ctx.settings?.invoiceCounter ?? 0,
+        }}
+      />
+    </div>
+  );
+}