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/autocomplete.go

@@ -0,0 +1,112 @@
+package tui
+
+import (
+	"strings"
+
+	"github.com/charmbracelet/lipgloss"
+	"github.com/lerko/nib/internal/db"
+)
+
+const maxSuggestions = 5
+
+type autocompleteModel struct {
+	suggestions []string
+	cursor      int
+	active      bool
+	prefix      string
+	tokenStart  int
+	tokenEnd    int
+}
+
+func (a *autocompleteModel) moveUp() {
+	if a.cursor > 0 {
+		a.cursor--
+	}
+}
+
+func (a *autocompleteModel) moveDown() {
+	if a.cursor < len(a.suggestions)-1 {
+		a.cursor++
+	}
+}
+
+func (a autocompleteModel) selected() string {
+	if len(a.suggestions) == 0 || a.cursor >= len(a.suggestions) {
+		return ""
+	}
+	return a.suggestions[a.cursor]
+}
+
+func (a autocompleteModel) visibleCount() int {
+	if len(a.suggestions) > maxSuggestions {
+		return maxSuggestions
+	}
+	return len(a.suggestions)
+}
+
+func (a autocompleteModel) view(width int) string {
+	if !a.active || len(a.suggestions) == 0 {
+		return ""
+	}
+
+	var b strings.Builder
+	n := a.visibleCount()
+	for i := 0; i < n; i++ {
+		tag := "#" + a.suggestions[i]
+		if i == a.cursor {
+			b.WriteString(acSelectedStyle.Render(" › " + tag))
+		} else {
+			b.WriteString(acItemStyle.Render("   " + tag))
+		}
+		if i < n-1 {
+			b.WriteString("\n")
+		}
+	}
+	if len(a.suggestions) > maxSuggestions {
+		b.WriteString("\n")
+		b.WriteString(acItemStyle.Render("   …"))
+	}
+
+	box := lipgloss.NewStyle().
+		Width(min(30, width)).
+		Render(b.String())
+	return box
+}
+
+func tagTokenAtCursor(val string, cursorPos int) (tokenStart, tokenEnd int, prefix string, ok bool) {
+	if cursorPos > len(val) {
+		cursorPos = len(val)
+	}
+
+	start := cursorPos
+	for start > 0 && val[start-1] != ' ' {
+		start--
+	}
+
+	if start >= len(val) || val[start] != '#' {
+		return 0, 0, "", false
+	}
+
+	end := cursorPos
+	for end < len(val) && val[end] != ' ' {
+		end++
+	}
+
+	prefix = strings.ToLower(val[start+1 : cursorPos])
+	return start, end, prefix, true
+}
+
+func filterTagSuggestions(tags []db.TagCount, prefix string) []string {
+	if prefix == "" {
+		return nil
+	}
+	prefix = strings.ToLower(prefix)
+	var result []string
+	for _, tc := range tags {
+		lower := strings.ToLower(tc.Tag)
+		if strings.HasPrefix(lower, prefix) && lower != prefix {
+			result = append(result, tc.Tag)
+		}
+	}
+	return result
+}