feat: keep empty cells consistent empty

DESIGN_DUIDELINES.md

@@ -293,6 +293,12 @@ Notes:
 - On **mobile**, sticky headers are not used; the layout uses normal flow (header and table scroll with the page) to preserve vertical space.
 - When the table is inside such a scroll container, use the CoreComponents table’s `sticky_header={true}` so the table’s `<thead>` stays sticky within the scroll area on desktop (`lg:sticky lg:top-0`, opaque background `bg-base-100`, z-index). Sticky areas must not overlap content at 200% zoom; focus order must remain header → filters → table.
 
+### 8.6 Empty table cells (missing values)
+- **MUST:** Missing values in tables are shown as **visually empty cells** (no dash, no "n/a").
+- **MUST NOT:** Use dashes ("-", "—", "–") or "n/a" as placeholders for empty cells.
+- **MUST:** For accessibility, render a screen-reader-only label so the cell is not announced as "blank". Use the CoreComponents `<.empty_cell sr_text="…">` for a cell that has no value, or `<.maybe_value value={…} empty_sr_text="…">` when the cell content is conditional (value present vs. absent).
+- **SHOULD:** Use context-specific `sr_text` where it helps (e.g. "No cycle", "No group assignment", "Not specified"). Default for "no value" is "Not specified".
+
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 ## 9) Flash / Toast messages (mandatory UX)