refactor(frontend): ApiError interface, tempIdSuffix rename, NET_GRID constants, extract onPaletteDrop handlers

ApiError: defined once in utils/api.ts, replaces 9 ad-hoc anonymous casts
across MazeNET, Inspector, DeckyFleet, SwarmHosts, Webhooks, PersonaGeneration,
ServiceConfigFields, CanaryTokens.

hex4 renamed to tempIdSuffix — the name now matches the comment that already
explained its purpose.

NET_GRID_{W,H,GAP,COLS} extracted from inline magic numbers to module-level
constants in MazeNET.tsx.

onPaletteDrop (130-line useCallback) split into three module-level handlers
(_dropNetwork, _dropArchetype, _dropService); the callback becomes a 10-line
router.

decnet_web/src/components/SwarmHosts.tsx

@@ -1,5 +1,5 @@
 import React, { useEffect, useRef, useState } from 'react';
-import api from '../utils/api';
+import api, { type ApiError } from '../utils/api';
 import EmptyState from './EmptyState/EmptyState';
 import Modal from './Modal/Modal';
 import './Dashboard.css';
@@ -108,7 +108,7 @@ const EnrollmentWizard: React.FC<EnrollmentWizardProps> = ({ open, onClose, onEn
       setResult(res.data);
       onEnrolled();
     } catch (err: unknown) {
-      const e = err as { response?: { data?: { detail?: string } } };
+      const e = err as ApiError;
       setError(e?.response?.data?.detail || 'Enrollment bundle creation failed');
     } finally {
       setSubmitting(false);