feat(reader): send end-anchor CFI for EPUB highlights

Web highlights stored only epubcfi_start, so devices received
degenerate pos0 == pos1 (zero-length) highlight ranges. The reader
now collapses the selection range to its end point for a second CFI
and stores it as epubcfi_end (PDF rect anchors reuse the JSON anchor
for both ends).

web/src/reader/reader.ts

@@ -412,6 +412,7 @@ document.addEventListener("alpine:init", () => {
       note: string;
       color: string;
       cfi: string;
+      cfiEnd: string;
       percentage: number;
       pdfPage: number;
       pdfRects: number[][];
@@ -443,6 +444,7 @@ document.addEventListener("alpine:init", () => {
       y: 0,
       text: "",
       cfi: "",
+      cfiEnd: "",
       id: "",
       color: "#ffd54f",
       note: "",
@@ -701,8 +703,15 @@ document.addEventListener("alpine:init", () => {
             const text = sel.toString().replace(/\s+/g, " ").trim();
             if (!text) return;
             let cfi: string;
+            let cfiEnd: string;
             try {
               cfi = this.view.getCFI(index, range);
+              // Collapse to the end point for a distinct end anchor —
+              // KOReader sync renders the highlight box from pos0/pos1, and
+              // pos1 == pos0 would be a degenerate (zero-length) range.
+              const endRange = range.cloneRange();
+              endRange.collapse(false);
+              cfiEnd = this.view.getCFI(index, endRange);
             } catch {
               return;
             }
@@ -715,6 +724,7 @@ document.addEventListener("alpine:init", () => {
               y: (iframeRect?.top ?? 0) + rect.top,
               text,
               cfi,
+              cfiEnd,
             });
           };
           doc.addEventListener(
@@ -827,6 +837,7 @@ document.addEventListener("alpine:init", () => {
           y: (iframeRect?.top ?? 0) + rect.top,
           text: h.text,
           cfi: h.cfi,
+          cfiEnd: h.cfiEnd,
           id: h.id,
           color: h.color,
           note: h.note,
@@ -1070,6 +1081,7 @@ document.addEventListener("alpine:init", () => {
       y: number;
       text: string;
       cfi: string;
+      cfiEnd?: string;
       id?: string;
       color?: string;
       note?: string;
@@ -1080,6 +1092,7 @@ document.addEventListener("alpine:init", () => {
       p.mode = opts.mode;
       p.text = opts.text;
       p.cfi = opts.cfi;
+      p.cfiEnd = opts.cfiEnd ?? "";
       p.id = opts.id ?? "";
       p.color = opts.color || "#ffd54f";
       p.note = opts.note ?? "";
@@ -1147,6 +1160,7 @@ document.addEventListener("alpine:init", () => {
         note: r.note_text ?? "",
         color: r.color ?? "#ffff00",
         cfi,
+        cfiEnd: r.epubcfi_end ?? "",
         percentage: r.percentage_start ?? 0,
         pdfPage,
         pdfRects,
@@ -1205,6 +1219,7 @@ document.addEventListener("alpine:init", () => {
               start_position: "",
               end_position: "",
               epubcfi_start: p.pdfPage >= 0 ? pdfAnchor : p.cfi,
+              epubcfi_end: p.pdfPage >= 0 ? pdfAnchor : p.cfiEnd,
               color,
               note_text: "",
               percentage_start: this.lastRelocateDetail?.fraction ?? 0,
@@ -1263,6 +1278,7 @@ document.addEventListener("alpine:init", () => {
               start_position: "",
               end_position: "",
               epubcfi_start: anchor,
+              epubcfi_end: p.pdfPage >= 0 ? anchor : p.cfiEnd,
               color: p.color,
               note_text: p.note,
             }),