fix(grzctl): handle empty submission states in TUI search results (#468)

Fixes #385 

TUI crashes with `ValueError: max() iterable argument is empty` when
displaying submissions that have no state updates yet.

**Changes:**
- Replace direct `max(submission.states, ...)` with existing
`submission.get_latest_state()` method which returns `None` for empty
states
- Display "missing" (styled as italic yellow) for "Latest State" and
"State Timestamp" columns when no states exist, matching the existing
pattern used elsewhere in the TUI

```python
# Before: crashes on empty states
latest_state = max(submission.states, key=lambda st: st.timestamp)

# After: graceful handling with styled "missing" text
latest_state = submission.get_latest_state()
self.add_row(
    submission.id,
    submission.pseudonym,
    latest_state.state if latest_state else rich.text.Text("missing", style="italic yellow"),
    latest_state.timestamp if latest_state else rich.text.Text("missing", style="italic yellow"),
)
```

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: tedil <7976289+tedil@users.noreply.github.com>

Author: Copilot

packages/grzctl/src/grzctl/commands/db/tui.py

@@ -245,8 +245,13 @@ async def search(
             submissions = session.exec(statement).all()
         logger.debug("Populating search table from the following statement: '%s'", str(statement))
         for submission in submissions:
-            latest_state = max(submission.states, key=lambda st: st.timestamp)
-            self.add_row(submission.id, submission.pseudonym, latest_state.state, latest_state.timestamp)
+            latest_state = submission.get_latest_state()
+            self.add_row(
+                submission.id,
+                submission.pseudonym,
+                latest_state.state if latest_state else rich.text.Text("missing", style="italic yellow"),
+                latest_state.timestamp if latest_state else rich.text.Text("missing", style="italic yellow"),
+            )
 
         self.loading = False