fix(plan): readable audit descriptions, project labels, dashboard invalidation, view-only & sticky-column UI

Work-plan fixes from this session:
- Czech audit descriptions for plan entries/overrides (was empty '-')
- server-embedded project label on grid cells (was '-' past the 100-project cap)
- dashboard activity + audit-log cache invalidation on plan mutations
- read-only cells: no '+' on empty, keep hover on cells with a record
- view modal: Czech category + formatted dates
- sticky date column made opaque (no bleed-through on horizontal scroll)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/utils/planAuditDescription.ts

@@ -0,0 +1,94 @@
+/**
+ * Human-readable Czech descriptions for work-plan audit-log rows.
+ *
+ * The audit log table ("Popis" column) shows only the `description` string,
+ * so it must be self-contained: who, when, what. Previously the plan routes
+ * left `description` undefined for normal edits, which rendered as "-" and
+ * made the audit rows useless. These helpers build a readable subject line
+ * such as: `Jan Novák · 08.06.2026 – 12.06.2026 · Práce · Projekt ABC`.
+ *
+ * Everything here is pure (no Prisma, no Date.now) so it is trivially unit
+ * testable. The service layer resolves user/project names and feeds plain
+ * strings in.
+ */
+
+/** Czech labels for the `plan_category` enum. Mirrors the frontend
+ * PlanCellModal options so the audit log reads the same as the UI. */
+export const PLAN_CATEGORY_LABELS_CS: Record<string, string> = {
+  work: "Práce",
+  preparation: "Příprava",
+  travel: "Cesta / Montáž",
+  leave: "Dovolená",
+  sick: "Nemoc",
+  training: "Školení",
+  other: "Jiné",
+};
+
+/** Translate a plan category to its Czech label, falling back to the raw
+ * value for unknown categories so nothing is ever silently dropped. */
+export function planCategoryLabel(category: string): string {
+  return PLAN_CATEGORY_LABELS_CS[category] ?? category;
+}
+
+/**
+ * Format a `YYYY-MM-DD` string as Czech `DD.MM.YYYY`.
+ *
+ * Takes a string (not a Date) on purpose: work-plan dates live in `@db.Date`
+ * columns and the service derives the ISO day via `toISOString().slice(0,10)`,
+ * so there is no timezone ambiguity to reintroduce here. Matches the
+ * `localDateCzStr` style in `src/utils/date.ts`.
+ */
+export function formatPlanDate(iso: string): string {
+  const [y, m, d] = iso.split("-");
+  if (!y || !m || !d) return iso;
+  return `${d}.${m}.${y}`;
+}
+
+export interface PlanAuditDescriptionInput {
+  /** Employee the plan row belongs to (display name). */
+  userName: string;
+  /** `plan_category` enum value. */
+  category: string;
+  /** Resolved project name, or null when the row has no project. */
+  projectName?: string | null;
+  /** Range start (YYYY-MM-DD). For overrides, pass the shift date here. */
+  dateFrom: string;
+  /** Range end (YYYY-MM-DD). For overrides/single days, equals `dateFrom`. */
+  dateTo: string;
+  /** Append "nouzová úprava" when the change bypassed the past-date lock. */
+  force?: boolean;
+  /** Extra Czech note appended at the end (e.g. "nahrazeno novým záznamem"). */
+  suffix?: string;
+}
+
+/**
+ * Build a Czech audit description: a `·`-separated subject line. The action
+ * (create/update/delete) and entity type are shown in their own audit-table
+ * columns, so the description carries only the subject — never the verb.
+ */
+export function buildPlanAuditDescription(
+  opts: PlanAuditDescriptionInput,
+): string {
+  const dateLabel =
+    opts.dateFrom === opts.dateTo
+      ? formatPlanDate(opts.dateFrom)
+      : `${formatPlanDate(opts.dateFrom)} – ${formatPlanDate(opts.dateTo)}`;
+
+  const parts: string[] = [
+    opts.userName,
+    dateLabel,
+    planCategoryLabel(opts.category),
+  ];
+
+  if (opts.projectName && opts.projectName.trim()) {
+    parts.push(opts.projectName.trim());
+  }
+  if (opts.suffix && opts.suffix.trim()) {
+    parts.push(opts.suffix.trim());
+  }
+  if (opts.force) {
+    parts.push("nouzová úprava");
+  }
+
+  return parts.join(" · ");
+}