feat: add ideation feature with per-tenant toggle

Adds idea submission capability gated by a per-tenant feature flag.
Super admins can enable/disable ideation for specific tenants via the
admin tenant detail drawer. Users see a lightbulb icon in the header
when enabled, opening a modal to submit ideas (title + description).
Ideas are stored in shared schema for cross-tenant backlog querying.

- Database: shared.ideas table (018-ideas.sql migration)
- Backend: Ideas NestJS module (entity, service, controller)
- Admin API: GET /admin/ideas, PUT /admin/ideas/:id/status,
  PUT /admin/organizations/:id/settings
- Frontend: IdeaModal component, lightbulb ActionIcon in header
- Admin UI: Feature Toggles card with ideation Switch in drawer

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/ideas/IdeaModal.tsx

@@ -0,0 +1,69 @@
+import { useState } from 'react';
+import { Modal, TextInput, Textarea, Button, Stack } from '@mantine/core';
+import { notifications } from '@mantine/notifications';
+import { useMutation } from '@tanstack/react-query';
+import api from '../../services/api';
+
+interface IdeaModalProps {
+  opened: boolean;
+  onClose: () => void;
+}
+
+export function IdeaModal({ opened, onClose }: IdeaModalProps) {
+  const [title, setTitle] = useState('');
+  const [description, setDescription] = useState('');
+
+  const submitIdea = useMutation({
+    mutationFn: async () => {
+      const { data } = await api.post('/ideas', { title, description });
+      return data;
+    },
+    onSuccess: () => {
+      notifications.show({ message: 'Idea submitted — thank you!', color: 'green' });
+      setTitle('');
+      setDescription('');
+      onClose();
+    },
+    onError: (err: any) => {
+      notifications.show({
+        message: err.response?.data?.message || 'Failed to submit idea',
+        color: 'red',
+      });
+    },
+  });
+
+  const handleClose = () => {
+    setTitle('');
+    setDescription('');
+    onClose();
+  };
+
+  return (
+    <Modal opened={opened} onClose={handleClose} title="Submit an Idea" size="md">
+      <Stack>
+        <TextInput
+          label="Title"
+          placeholder="Brief summary of your idea"
+          required
+          value={title}
+          onChange={(e) => setTitle(e.currentTarget.value)}
+          maxLength={255}
+        />
+        <Textarea
+          label="Description"
+          placeholder="Describe your idea in more detail (optional)"
+          minRows={4}
+          value={description}
+          onChange={(e) => setDescription(e.currentTarget.value)}
+        />
+        <Button
+          onClick={() => submitIdea.mutate()}
+          loading={submitIdea.isPending}
+          disabled={!title.trim()}
+        >
+          Submit Idea
+        </Button>
+      </Stack>
+    </Modal>
+  );
+}