fix: use ebookProgress field for ebook reading progress

[OnlyTerp]

Fixes #162

Problem

ShelfBridge reads progress instead of ebookProgress for ebooks, causing ebook reading progress to always show as 0%.

Root Cause

The previous fix (PR #164) used nullish coalescing (??) to fall back from progressData.progress to progressData.ebookProgress. However, for ebooks the ABS API returns progress: 0 (not null or undefined), so ?? never triggered the fallback — 0 ?? ebookProgress returns 0.

The media type detection (isEbook) also had fragility issues — if media.ebookFile wasn't detected correctly (e.g., dual-format items, unexpected API structure), the code would take the audiobook path and never check ebookProgress.

Fix

1. Progress field selection (src/audiobookshelf-client.js)

Matches ABS's own client logic: if progress is falsy (0) and ebookProgress > 0, use ebookProgress. This completely avoids relying on media type detection for choosing the right progress field.

\\js
// Before (broken): 0 ?? ebookProgress === 0
const rawProgress = isEbook
? (progressData.ebookProgress ?? progressData.progress)
: (progressData.progress ?? progressData.ebookProgress);

// After (matches ABS client): 0 is falsy, so ebookProgress is used
const rawProgress = (!progressData.progress && progressData.ebookProgress > 0)
? progressData.ebookProgress
: (progressData.progress || 0);
\\

2. Ebook format detection (src/matching/utils/audiobookshelf-extractor.js)

• Uses has_ebook_progress (derived from ebookProgress > 0) as the strongest signal for ebook format detection, overriding fragile mediaType/media.ebookFile checks
• Handles dual-format items (both ebookFile and audioFiles) by checking which format has actual user progress

Changes

File	What changed
src/audiobookshelf-client.js	Progress field selection matches ABS client logic; stores has_ebook_progress and ebook_location on item data
src/matching/utils/audiobookshelf-extractor.js	has_ebook_progress as top-priority format signal; dual-format item handling

Testing

• All 124 existing tests pass ✅
• All 26 completion detection tests pass ✅
• No new dependencies
• Minimal, focused diff (2 files, ~35 lines changed)