Fix inconsistent and confusing project statistics display

Backend:
- Count print job records instead of summing quantities for stats
- Include "archived" status as successful (completed + archived)
- Include all failure states (failed, aborted, cancelled, stopped)
- Add completed_count and failed_count to ProjectListResponse

Frontend ProjectsPage:
- Show completed_count instead of total_items in progress displays
- Progress bar now shows "X / Y completed" to match percentage
- Add failed count indicator (red) when failures exist
- Footer stats show completed (green checkmark) and failed (red) separately

Frontend ProjectDetailPage:
- Replace confusing "Total Items" card with "Print Jobs" card
- Show "X successful" as main value, "Y failed" below in red
- Show "Z in progress" in yellow for unfinished prints
- Progress bar text changed from "items" to "completed"
- Add hint prop to StatCard component for tooltips

This ensures stats are consistent between:
- Project list page and detail page
- Stats cards and archive list counts
- Progress percentages and displayed fractions

Fixes #85

frontend/src/api/client.ts

@@ -412,7 +412,9 @@ export interface ProjectListItem {
   target_count: number | null;
   created_at: string;
   archive_count: number;  // Number of print jobs
-  total_items: number;  // Sum of quantities (total items printed)
+  total_items: number;  // Sum of quantities (total items printed, including failed)
+  completed_count: number;  // Sum of quantities for completed prints only
+  failed_count: number;  // Sum of quantities for failed prints
   queue_count: number;
   progress_percent: number | null;
   archives: ArchivePreview[];