feat(tui): add tag autocomplete and query composition

Tag autocomplete shows suggestions when typing #partial in capture bar.
Tab/enter accepts, up/down navigates, esc dismisses.

Query composition extends ? search with date filters (@today, @week,
@month, <7d, >30d), card type filters (^snippet), all composable
with existing text and tag filters.

internal/tui/styles.go

@@ -41,6 +41,8 @@ var (
 	railActiveTagStyle  lipgloss.Style
 	railCountStyle      lipgloss.Style
 	stumbleAgeStyle     lipgloss.Style
+	acSelectedStyle     lipgloss.Style
+	acItemStyle         lipgloss.Style
 )
 
 func init() {
@@ -96,4 +98,6 @@ func applyTheme() {
 	railActiveTagStyle = lipgloss.NewStyle().Foreground(ok).Bold(true)
 	railCountStyle = lipgloss.NewStyle().Foreground(dim)
 	stumbleAgeStyle = lipgloss.NewStyle().Foreground(remind)
+	acSelectedStyle = lipgloss.NewStyle().Foreground(accent).Bold(true)
+	acItemStyle = lipgloss.NewStyle().Foreground(muted)
 }