chore(server): delete dead ParseEbook 501 placeholder

Born dead in e7ce0cb (2026-04-03, backend reader infrastructure):
the "Phase 2.5" plan assumed MOBI/AZW3/DOCX/RTF would need server-side
parsing, so ParseEbook was written as the endpoint that would do it —
but it only ever returned 501 "not yet implemented", and no route in
router/reader.go ever pointed at it. No caller in Go, templates, or
web JS/TS ever existed either.

The eventual architecture never needed it: the web reader hands the
raw file to foliate-js and parses client-side (MOBI renders via the
fork's mobi.js — verified live; DOCX via mammoth; RTF/PDB shipped).
By now it was also stale — it 501'd DOCX/RTF as "not yet implemented"
while both work, and offered an AZW3 path that was dropped entirely.

Pure deletion: no route registration, no references, no tests, no
behavior change. go build ./... clean.

internal/handlers/reader.go

@@ -590,57 +590,6 @@ func (h *ReaderHandler) generatePDFThumbnail(fullPath string, page int, width, h
 	return []byte{}, nil
 }
 
-func (h *ReaderHandler) ParseEbook(c *echo.Context) error {
-	mediaItemID := c.Param("mediaItemId")
-	parsedUUID, err := uuid.Parse(mediaItemID)
-	if err != nil {
-		return c.JSON(400, map[string]string{"error": "Invalid media item ID"})
-	}
-
-	// Fetch media item
-	mediaItem, err := h.db.GetMediaItem(c.Request().Context(), pgtype.UUID{Bytes: parsedUUID, Valid: true})
-	if err != nil {
-		if errors.Is(err, pgx.ErrNoRows) {
-			return c.JSON(404, map[string]string{"error": "Media item not found"})
-		}
-		return c.JSON(500, map[string]string{"error": "Failed to fetch media item"})
-	}
-
-	// Check if format requires server-side parsing
-	requiresServerParsing := false
-	formatName := ""
-	switch mediaItem.MimeType.String {
-	case "application/x-mobipocket-ebook":
-		requiresServerParsing = true
-		formatName = "MOBI"
-	case "application/vnd.amazon.mobi8-ebook":
-		requiresServerParsing = true
-		formatName = "AZW3/KF8"
-	case "application/vnd.openxmlformats-officedocument.wordprocessingml.document":
-		requiresServerParsing = true
-		formatName = "DOCX"
-	case "application/rtf":
-		requiresServerParsing = true
-		formatName = "RTF"
-	}
-
-	if requiresServerParsing {
-		// Phase 1: Return 501 for server-side formats
-		return c.JSON(501, map[string]interface{}{
-			"error":      fmt.Sprintf("Server-side %s parsing is not yet implemented", formatName),
-			"message":    fmt.Sprintf("%s format support is planned for Phase 2.5", formatName),
-			"suggestion": "Please convert your ebook to EPUB format for now",
-			"format":     formatName,
-			"phase":      "2.5",
-		})
-	}
-
-	// Client-side format - should not call this endpoint
-	return c.JSON(400, map[string]string{
-		"error": "This format should be parsed client-side, not on the server",
-	})
-}
-
 // ShouldTreatAsComic reports whether a fixed-layout item that lives in a
 // comics or manga library should get comic reader treatment: bookmarks
 // only — no text-selection highlights, no annotations, no in-book search.