feat: add Filament admin panel with migrations and design spec

- Add AdminPanelProvider mounting panel at `/admin` with `is_admin` auth guard
- Add `is_admin` boolean column to users table
- Add brent_prices and price_predictions tables with appropriate indexes
- Add comprehensive admin design spec covering resources, dashboard, navigation, and build order
- Configure default panel with amber primary color and standard middleware stack
- Add compiled Filament assets (actions.js, app.css)

public/js/filament/actions/actions.js

@@ -0,0 +1 @@
+(()=>{var n=({livewireId:e})=>({actionNestingIndex:null,init(){window.addEventListener("sync-action-modals",t=>{t.detail.id===e&&this.syncActionModals(t.detail.newActionNestingIndex,t.detail.shouldOverlayParentActions??!1)})},syncActionModals(t,i=!1){if(this.actionNestingIndex===t){this.actionNestingIndex!==null&&this.$nextTick(()=>this.openModal());return}let s=this.actionNestingIndex!==null&&t!==null&&t>this.actionNestingIndex;if(this.actionNestingIndex!==null&&!(i&&s)&&this.closeModal(),this.actionNestingIndex=t,this.actionNestingIndex!==null){if(!this.$el.querySelector(`#${this.generateModalId(t)}`)){this.$nextTick(()=>this.openModal());return}this.openModal()}},generateModalId(t){return`fi-${e}-action-`+t},openModal(){let t=this.generateModalId(this.actionNestingIndex);document.dispatchEvent(new CustomEvent("open-modal",{bubbles:!0,composed:!0,detail:{id:t}}))},closeModal(){let t=this.generateModalId(this.actionNestingIndex);document.dispatchEvent(new CustomEvent("close-modal-quietly",{bubbles:!0,composed:!0,detail:{id:t}}))}});document.addEventListener("alpine:init",()=>{window.Alpine.data("filamentActionModals",n)});})();