fix: resolve all JS architecture violations (JS-005 through JS-009)
Fixed 89 violations across vendor, admin, and shared JavaScript files:
JS-008 (raw fetch → apiClient):
- Added postFormData() and getBlob() methods to api-client.js
- Updated inventory.js, messages.js to use apiClient.postFormData()
- Added noqa for file downloads that need response headers
JS-009 (window.showToast → Utils.showToast):
- Updated admin/messages.js, notifications.js, vendor/messages.js
- Replaced alert() in customers.js
JS-006 (async error handling):
- Added try/catch to all async init() and reload() methods
- Fixed vendor: billing, dashboard, login, messages, onboarding
- Fixed shared: feature-store, upgrade-prompts
- Fixed admin: all page components
JS-005 (init guards):
- Added initialization guards to prevent duplicate init() calls
- Pattern: if (window._componentInitialized) return;
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>