feat(tui): include backlinks in link picker

Link picker now shows both outgoing [[links]] and backlinks in
a unified list with section headers. Backlinks follow by entity
ID directly, outgoing links resolve by text. Navigating into a
backlink works the same as following an outgoing link — pushes
to nav stack, esc pops back.

internal/tui/linkpicker.go

@@ -3,25 +3,52 @@ package tui
 import (
 	"strings"
 
+	"github.com/lerko/nib/internal/db"
 	"github.com/lerko/nib/internal/link"
 )
 
+type linkKind int
+
+const (
+	linkOutgoing linkKind = iota
+	linkBacklink
+)
+
+type linkItem struct {
+	text     string
+	entityID string
+	kind     linkKind
+}
+
 type linkPickerModel struct {
-	links  []string
+	items  []linkItem
 	cursor int
 }
 
-func newLinkPicker(body string) linkPickerModel {
-	return linkPickerModel{
-		links: link.ExtractLinks(body),
+func newLinkPicker(body string, backlinks []db.Backlink) linkPickerModel {
+	var items []linkItem
+
+	for _, lt := range link.ExtractLinks(body) {
+		items = append(items, linkItem{text: lt, kind: linkOutgoing})
 	}
+	for _, bl := range backlinks {
+		label := bl.Body
+		if bl.Title != nil {
+			label = *bl.Title
+		} else if len(label) > 50 {
+			label = label[:50] + "…"
+		}
+		items = append(items, linkItem{text: label, entityID: bl.EntityID, kind: linkBacklink})
+	}
+
+	return linkPickerModel{items: items}
 }
 
-func (lp linkPickerModel) selected() string {
-	if len(lp.links) == 0 || lp.cursor >= len(lp.links) {
-		return ""
+func (lp linkPickerModel) selected() linkItem {
+	if len(lp.items) == 0 || lp.cursor >= len(lp.items) {
+		return linkItem{}
 	}
-	return lp.links[lp.cursor]
+	return lp.items[lp.cursor]
 }
 
 func (lp linkPickerModel) update(key string) linkPickerModel {
@@ -31,7 +58,7 @@ func (lp linkPickerModel) update(key string) linkPickerModel {
 			lp.cursor--
 		}
 	case "down", "j":
-		if lp.cursor < len(lp.links)-1 {
+		if lp.cursor < len(lp.items)-1 {
 			lp.cursor++
 		}
 	}
@@ -42,15 +69,31 @@ func (lp linkPickerModel) view(width int) string {
 	var b strings.Builder
 	b.WriteString(titleStyle.Render("follow link") + "\n\n")
 
-	if len(lp.links) == 0 {
-		b.WriteString(hintDescStyle.Render("  no [[links]] in this entry"))
+	if len(lp.items) == 0 {
+		b.WriteString(hintDescStyle.Render("  no links or backlinks"))
 		b.WriteString("\n\n")
 		b.WriteString(helpStyle.Render("esc:back"))
 		return b.String()
 	}
 
-	for i, lt := range lp.links {
-		label := "[[" + lt + "]]"
+	prevKind := linkKind(-1)
+	for i, item := range lp.items {
+		if item.kind != prevKind {
+			if item.kind == linkOutgoing {
+				b.WriteString(dateHeaderStyle.Render("── outgoing ──") + "\n")
+			} else {
+				b.WriteString(dateHeaderStyle.Render("── backlinks ──") + "\n")
+			}
+			prevKind = item.kind
+		}
+
+		var label string
+		if item.kind == linkOutgoing {
+			label = "[[" + item.text + "]]"
+		} else {
+			label = "← " + item.text
+		}
+
 		if i == lp.cursor {
 			b.WriteString(selectedItemStyle.Render(" " + label))
 		} else {