feat(reader): wire up progress mode switching with four display modes

Connect the existing progress_mode setting dropdown to the reader's
progress display. Four modes are now functional:
- pages: overall percent + page/location number (default, existing)
- chapter: chapter title + page X / Y within current section
- percentage: overall percent only
- time-left: percent + estimated time remaining via reading speed API
The progress display in the bottom bar is now clickable to cycle through
modes with immediate visual feedback. The settings dropdown is bound
with x-model for persistence. Reading speed is fetched once on init
from the backend reading-speed API for time-left estimates.

templates/reader.templ

@@ -154,7 +154,7 @@ templ ReaderChrome(user User, metadata ReaderMetadata, progress ReadingProgress)
 				<!-- Separator -->
 				<div class="w-px h-6 bg-gray-600 mx-1"></div>
 				<!-- Progress display -->
-				<div id="progress-display" x-text="progressText" data-progress-mode="pages" class="text-sm min-w-[4rem] text-center">
+				<div id="progress-display" x-text="progressText" @click="cycleProgressMode()" title="Click to change progress mode" class="text-sm min-w-[4rem] text-center cursor-pointer">
 					if progress.FormatGroup == "reflowable" {
 						if metadata.EstimatedPages > 0 {
 							{ fmt.Sprintf("%.0f%% · Page %d/%d", progress.Percentage, progress.CurrentPage, metadata.EstimatedPages) }
@@ -205,7 +205,7 @@ templ ReaderSettingsPanel() {
 				</label>
 				<label class="block mb-2">
 					Progress Mode
-					<select name="progress_mode" class="w-full mt-1 px-3 py-2 rounded border">
+					<select name="progress_mode" x-model="progressMode" @change="applyProgressMode()" class="w-full mt-1 px-3 py-2 rounded border">
 						<option value="pages">Pages</option>
 						<option value="chapter">Chapter</option>
 						<option value="percentage">Percentage</option>