Show a muted "in sync" for submodules without issues

An empty status cell could be read as missing data. The muted word
confirms the check ran without drawing attention. The word is defined
once in the theme and shared with the detail pane.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/requirements.md

@@ -42,7 +42,8 @@ commit hashes. It doesn't answer the questions users actually have:
 ### State per submodule
 
 - **F10** Each submodule shows at most **one** state word: the most severe
-  issue, plus `+n` if there are more. Submodules without issues show no word.
+  issue, plus `+n` if there are more. Submodules without issues show a
+  muted `in sync`.
   See [state-model.md](state-model.md) for the full rules.
 - **F11** Each submodule shows its pin as a ref (`origin/main`, a tag, or a
   short SHA as a fallback) and the distance to that ref (`↑n`, `↓n`, `↑n↓m`).

docs/ux-guide.md

@@ -47,13 +47,15 @@ indent ▸ name [n]   status          ref             delta
 | indent | 2 per depth | |
 | toggle | 3 | `▸` collapsed, `▾` expanded, blank for leaves |
 | name | fits the widest visible name | name, `[n]` = direct children (collapsed only) |
-| status | 14 | issue word, `+n`, `·k` hidden issues; spinner while loading |
+| status | 14 | issue word, `+n`, `·k` hidden issues; muted `in sync` without issues; spinner while loading |
 | ref | widest ref, max 22 | resolved ref; muted short SHA if unresolved |
 | delta | 6 | `↑n`, `↓n`, `↑n↓m` |
 
 - The name column is only as wide as needed, so states stay close to names.
 - Directory headers (`src/`, `modules/`) are muted and not selectable.
-- Rows without issues: name and ref muted (except the selected row).
+- Rows without issues: name and ref muted (except the selected row), status
+  `in sync` in muted grey. An empty status cell would look like missing
+  data; the muted word confirms the check ran without drawing attention.
 
 ### Detail pane