refactor(webui): extract repeated dashboard elements into shared components

Markup and helpers that were copied between pages now live in one
place:
- ChartCard, StatDisabledAlert, StatItem, DetailField, BudgetRatioBars,
  LabeledSelect, TargetPicker and LoadStateView components
- lib/scope.ts, lib/columns.ts and lib/chart-palette.ts
- messageOf, isAuthRejection, and the USD to micro-USD conversion
  helpers
- one monthly cost projection, one date formatter, and the
  useCopyFeedback composable

Behaviour is unchanged. Before and after screenshots of every page
match at 390 and 1440 px. Empty-state text now comes from the shared
EmptyState component, and the user run-out date uses the short date
format. admin_assets_gen.go is regenerated.

Claude-Session: https://claude.ai/code/session_01V5jYJNxpDFdJkyyExpADrv

webui/src/composables/useCopyFeedback.ts

@@ -0,0 +1,42 @@
+import { onUnmounted, ref, type Ref } from 'vue'
+
+/** RESET_MS is how long a copy-feedback state (`copied`/`selected`/`failed`) stays visible before reverting to `idle` — SnippetBlock.vue's and ModelChip.vue's own identical 1500ms. */
+const RESET_MS = 1500
+
+/** CopyFeedbackState mirrors lib/clipboard.ts's copyText own return union, plus the resting `idle` state neither SnippetBlock.vue nor ModelChip.vue had a name for before this composable. */
+export type CopyFeedbackState = 'idle' | 'copied' | 'selected' | 'failed'
+
+export interface UseCopyFeedback {
+  /** The current feedback state — drives a caller's own icon/label swap. */
+  state: Ref<CopyFeedbackState>
+  /** Records a copyText() outcome and schedules the reset-to-idle timer, clearing any still-pending one first (a rapid double-click restarts the window rather than stacking two timers). */
+  set: (result: 'copied' | 'selected' | 'failed') => void
+}
+
+/**
+ * useCopyFeedback (reuse-audit.md F10) is the ONE "show a transient copy
+ * outcome, then revert to idle after 1500ms" composable SnippetBlock.vue
+ * and ModelChip.vue used to each hand-roll — the same `state` ref/
+ * `resetTimer`/`clearTimeout`-on-unmount triple, with the identical
+ * 1500ms magic number declared independently in both. Calls
+ * `onUnmounted` itself (this composable is only ever invoked from a
+ * component's own `setup()`/`<script setup>`, same as every other
+ * composable in this panel), so a caller no longer needs its own cleanup
+ * hook just for this timer.
+ */
+export function useCopyFeedback(): UseCopyFeedback {
+  const state = ref<CopyFeedbackState>('idle')
+  let resetTimer: ReturnType<typeof setTimeout> | undefined
+
+  function set(result: 'copied' | 'selected' | 'failed'): void {
+    state.value = result
+    clearTimeout(resetTimer)
+    resetTimer = setTimeout(() => {
+      state.value = 'idle'
+    }, RESET_MS)
+  }
+
+  onUnmounted(() => clearTimeout(resetTimer))
+
+  return { state, set }
+}