feat(backend): favourite, chapter override, and delete fragments

Adds the three UI mutation endpoints (favourite toggle, manual chapter
override, delete) plus the card controls that call them via htmx.
Each mutation is a read-modify-write through Store.Get/Upsert so
Upsert alone decides whether updated_at moves — favouriting must not
reorder the list, only real reading progress should.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/web.go

@@ -8,6 +8,7 @@ import (
 	"log"
 	"net/http"
 	"strconv"
+	"strings"
 	"time"
 )
 
@@ -66,6 +67,9 @@ func (h *webHandler) register(mux *http.ServeMux) {
 	mux.Handle("GET /static/", staticHandler())
 
 	mux.HandleFunc("GET /ui/list", h.requireSession(h.uiList))
+	mux.HandleFunc("POST /ui/bookmarks/{key}/favorite", h.requireSession(h.uiFavorite))
+	mux.HandleFunc("POST /ui/bookmarks/{key}/chapter", h.requireSession(h.uiChapter))
+	mux.HandleFunc("DELETE /ui/bookmarks/{key}", h.requireSession(h.uiDelete))
 }
 
 // staticHandler serves the embedded assets. The vendored htmx build and the
@@ -199,3 +203,94 @@ func (h *webHandler) logout(w http.ResponseWriter, r *http.Request) {
 	clearSessionCookie(w, r)
 	http.Redirect(w, r, "/", http.StatusSeeOther)
 }
+
+// loadForMutation fetches the row a mutation targets, writing the error
+// response itself when there is nothing to mutate.
+func (h *webHandler) loadForMutation(w http.ResponseWriter, r *http.Request) (Bookmark, bool) {
+	key := r.PathValue("key")
+	if key == "" {
+		http.Error(w, "missing key", http.StatusBadRequest)
+		return Bookmark{}, false
+	}
+	b, ok, err := h.store.Get(key)
+	if err != nil {
+		log.Printf("ui get %q: %v", key, err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
+		return Bookmark{}, false
+	}
+	if !ok {
+		http.Error(w, "not found", http.StatusNotFound)
+		return Bookmark{}, false
+	}
+	return b, true
+}
+
+// saveAndRenderCard upserts and renders the row as stored. Upsert decides
+// whether updated_at moves, so the argument's timestamp is only a candidate and
+// the response must come from the return value.
+func (h *webHandler) saveAndRenderCard(w http.ResponseWriter, b Bookmark) {
+	stored, err := h.store.Upsert(b)
+	if err != nil {
+		log.Printf("ui upsert %q: %v", b.Key, err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
+		return
+	}
+	h.render(w, http.StatusOK, "card", stored)
+}
+
+// uiFavorite flips the favourite flag. last_chapter_num is untouched, so
+// Upsert keeps the stored updated_at and the list does not reorder.
+func (h *webHandler) uiFavorite(w http.ResponseWriter, r *http.Request) {
+	b, ok := h.loadForMutation(w, r)
+	if !ok {
+		return
+	}
+	b.Favorite = !b.Favorite
+	b.UpdatedAt = time.Now().UnixMilli()
+	h.saveAndRenderCard(w, b)
+}
+
+// uiChapter forces the read chapter to a value the user typed.
+//
+// It clears last_chapter_url: that URL points at the chapter actually read, and
+// once the number is forced elsewhere it would send the reader backwards.
+// ContinueURL then falls back to the series page, which is always right.
+func (h *webHandler) uiChapter(w http.ResponseWriter, r *http.Request) {
+	b, ok := h.loadForMutation(w, r)
+	if !ok {
+		return
+	}
+	if err := r.ParseForm(); err != nil {
+		http.Error(w, "invalid form", http.StatusBadRequest)
+		return
+	}
+	raw := strings.TrimSpace(r.PostFormValue("chapter"))
+	num, err := strconv.ParseFloat(raw, 64)
+	if err != nil || num < 0 {
+		http.Error(w, "chapter must be a non-negative number", http.StatusBadRequest)
+		return
+	}
+
+	b.LastChapter = raw
+	b.LastChapterNum = num
+	b.LastChapterURL = ""
+	b.UpdatedAt = time.Now().UnixMilli()
+	h.saveAndRenderCard(w, b)
+}
+
+// uiDelete removes the row and answers with an empty body, which htmx swaps in
+// place of the card — removing it from the page.
+func (h *webHandler) uiDelete(w http.ResponseWriter, r *http.Request) {
+	key := r.PathValue("key")
+	if key == "" {
+		http.Error(w, "missing key", http.StatusBadRequest)
+		return
+	}
+	if err := h.store.Delete(key); err != nil {
+		log.Printf("ui delete %q: %v", key, err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	w.WriteHeader(http.StatusOK)
+}