feat(tui): stumble mode — resurface stale entries card by card

Card-by-card walkthrough of entries untouched for 30+ days.
Prevents write-mostly decay by bringing old entries back to attention.

- S from list triggers stumble, loads entries where modified_at < 30d
- Single-card view with markdown body, glyph, tags, age indicator
- Actions: n skip, d dismiss, ! pin, p promote, m absorb, esc exit
- Progress indicator: stumble [3/12]
- After promote/absorb from stumble, returns to deck (not list)
- "All caught up" screen when deck exhausted
- DB: add ModifiedBefore to ListParams, modified_at sort column

internal/tui/statusbar.go

@@ -82,6 +82,8 @@ func contextHints(m model) []hint {
 		return []hint{{"j/k", "nav"}, {"enter", "select"}, {"esc", "cancel"}}
 	case stateAbsorb:
 		return []hint{{"j/k", "nav"}, {"enter", "absorb"}, {"esc", "cancel"}}
+	case stateStumble:
+		return []hint{{"n", "skip"}, {"d", "dismiss"}, {"!", "pin"}, {"p", "promote"}, {"m", "absorb"}, {"esc", "quit"}}
 	}
 
 	switch m.focus {