feat(kanban): badges done/locked + drag locked en mismo column + migrations + UX stickers

- badges: locked → tiempo bloqueado; done → fecha completion + total lead time; otherwise → tiempo en columna
- locked cards: drag permitido dentro de mismo column (cross-column rejected con notification)
- card field: locked_at desde JOIN card_lock_history (open period)
- migrations: refactor a embed.FS, archivos 002-005 extraidos de ensureColumns; ensureColumns queda como backstop
- stickers UX: opacidad 1, debajo del texto, picker estable (useRef), boton entra directo a modo con 😀, popover cierra outside, cards done filter brightness
- format: formatDateTimeShort

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/App.tsx

@@ -423,6 +423,12 @@ export function App() {
     // Card drag
     const destCol = resolveColumnId(overId);
     if (!destCol) return;
+    const activeCard = board.cards.find((c) => c.id === activeId);
+    if (activeCard?.locked && activeCard.column_id !== destCol) {
+      notifications.show({ color: "yellow", message: "Card bloqueada: no se puede mover entre columnas" });
+      reload();
+      return;
+    }
     const destCards = board.cards
       .filter((c) => c.column_id === destCol)
       .sort((a, b) => a.position - b.position);
@@ -1108,7 +1114,13 @@ export function App() {
                     variant={activeSticker ? "filled" : "default"}
                     color={activeSticker ? "yellow" : undefined}
                     leftSection={<IconMoodSmile size={14} />}
-                    onClick={() => setStickerPickerOpen((v) => !v)}
+                    onClick={() => {
+                      if (!activeSticker) {
+                        setActiveSticker("😀");
+                      } else {
+                        setStickerPickerOpen((v) => !v);
+                      }
+                    }}
                   >
                     {activeSticker ? `Modo sticker: ${activeSticker}` : "Stickers"}
                   </Button>