feat(projects): gated project pickers on quote/contract/hours editors

- ProjectSelect: a reusable picker that renders nothing when the projects
  flag is off (satisfies 'book to project hidden unless projects enabled').
- projects.service.ts: full frontend API client (list/get/create/update,
  overview, assign event/quote/contract, email preview + 4 actions).
- Quote + contract editors carry an optional projectId (state, prefill,
  payload); service payload/detail types updated.
- HoursSection gains a 'book to project' control; backend createEntry
  persists project_id (migration 118, hasColumnCached guarded).

frontend/src/pages/admin/contracts/ContractEditorPage.tsx

@@ -24,6 +24,7 @@ import {
   CONTRACT_SECTIONS,
 } from '../../../services/contracts.service';
 import { CustomerPicker } from '../../../components/admin/CustomerPicker';
+import { ProjectSelect } from '../../../components/admin/ProjectSelect';
 
 interface BlockRow {
   blockId: number;
@@ -63,6 +64,7 @@ export const ContractEditorPage: React.FC = () => {
   const [language, setLanguage] = useState('de');
   const [issueDate, setIssueDate] = useState(() => new Date().toISOString().slice(0, 10));
   const [validUntil, setValidUntil] = useState('');
+  const [projectId, setProjectId] = useState<number | null>(null);
   const [blocks, setBlocks] = useState<BlockRow[]>([]);
 
   // Load existing contract on edit.
@@ -110,6 +112,7 @@ export const ContractEditorPage: React.FC = () => {
     setLanguage(c.language || 'de');
     setIssueDate(c.issueDate);
     setValidUntil(c.validUntil || '');
+    setProjectId(c.projectId ?? null);
     setBlocks((c.inclusions || []).map((inc) => ({
       blockId: inc.blockId,
       section: inc.section,
@@ -188,6 +191,7 @@ export const ContractEditorPage: React.FC = () => {
         outroText: outroText || null,
         issueDate,
         validUntil: validUntil || undefined,
+        projectId: projectId ?? null,
       });
       // Apply block toggles + ordering as an update right after create.
       await contractsService.update(created.contract.id, {
@@ -220,6 +224,7 @@ export const ContractEditorPage: React.FC = () => {
         language,
         issueDate,
         validUntil: validUntil || undefined,
+        projectId: projectId ?? null,
         blocks: blocks.map((b) => ({
           blockId: b.blockId, included: b.included, position: b.position,
         })),
@@ -348,6 +353,16 @@ export const ContractEditorPage: React.FC = () => {
           </div>
         )}
 
+        {/* Project link (renders only when the projects feature is on). */}
+        <div className="mb-4">
+          <ProjectSelect
+            label={t('projects.picker.label', 'Project') as string}
+            value={projectId}
+            customerAccountId={customerAccountId}
+            onChange={setProjectId}
+          />
+        </div>
+
         <div className="grid grid-cols-1 md:grid-cols-2 gap-3">
           <div>
             <label className="block text-sm font-medium mb-1">

frontend/src/pages/admin/quotes/QuoteEditorPage.tsx

@@ -24,6 +24,7 @@ import {
 } from '../../../services/quotes.service';
 import { LineItemsTable, type EditableLineItem } from '../../../components/admin/LineItemsTable';
 import { CustomerPicker } from '../../../components/admin/CustomerPicker';
+import { ProjectSelect } from '../../../components/admin/ProjectSelect';
 import { InstallmentsPanel } from '../../../components/admin/InstallmentsPanel';
 import { customerAdminService } from '../../../services/customerAdmin.service';
 import { userManagementService } from '../../../services/userManagement.service';
@@ -59,6 +60,8 @@ interface FormState {
   internalNotes: string;
   ccPdfEmail: string;
   businessBankAccountId: number | null;
+  /** Migration 121 — optional Project Overview link. */
+  projectId: number | null;
   lineItems: EditableLineItem[];
   // Ad-hoc installments (commit #6). null = use the payment-timing
   // template's installments; array = explicit per-quote override.
@@ -88,6 +91,7 @@ const empty: FormState = {
   internalNotes: '',
   ccPdfEmail: '',
   businessBankAccountId: null,
+  projectId: null,
   lineItems: [],
   installments: null,
 };
@@ -123,6 +127,8 @@ function buildPayload(f: FormState): QuoteCreatePayload {
     internalNotes: f.internalNotes || undefined,
     ccPdfEmail: f.ccPdfEmail || undefined,
     businessBankAccountId: f.businessBankAccountId || undefined,
+    // Migration 121 — Project Overview link. Send null to clear.
+    projectId: f.projectId ?? null,
     lineItems: f.lineItems.map((li) => ({
       position: li.position,
       quantity: li.quantity,
@@ -214,6 +220,7 @@ export const QuoteEditorPage: React.FC = () => {
         internalNotes: q.internalNotes || '',
         ccPdfEmail: q.ccPdfEmail || '',
         businessBankAccountId: q.businessBankAccountId,
+        projectId: q.projectId ?? null,
         lineItems: existing.lineItems.map((li) => ({
           id: li.id,
           position: li.position,
@@ -479,6 +486,15 @@ export const QuoteEditorPage: React.FC = () => {
           }))}
           searchPlaceholder={t('quotes.customerSearch', 'Search customer by email or company…') as string}
         />
+        {/* Project link (renders only when the projects feature is on). */}
+        <div className="mt-3">
+          <ProjectSelect
+            label={t('projects.picker.label', 'Project') as string}
+            value={form.projectId}
+            customerAccountId={form.customerAccountId}
+            onChange={(projectId) => setForm((f) => ({ ...f, projectId }))}
+          />
+        </div>
       </Card>
 
       {/* Section: Event */}