switch to table, optimize status, and more

[andiwand]

1. Flat table instead of nested collapsible list

• One row per comparable file (and per missing file/dir), columns: Status · Path · Message · Actions.
• Path is the full relative path in a monospace font, so the hierarchy is readable without nesting.
• Rows are sorted by path. Comparable files link to the side-by-side compare view as before.

2. Fixed the slow loading (the main culprit)

• The old code was roughly O(n²): generate_tree recursed, and for every entry it called Comparator.result(path) and result(path.parent). For directories result() recursively re-walked the entire subtree (with repeated iterdir() disk I/O) to aggregate a status — recomputed from scratch on each page load.
• Now there's a single O(n) walk (collect()), and each file's status is an O(1) dict lookup. No per-directory aggregation, no parent re-checks. I dropped directory rows entirely since the full path already conveys structure.

3. Live status updates (async-friendly)

• Comparisons run in the background, so I added a lightweight /status JSON endpoint (Comparator.all_results() — a plain dict snapshot, no tree walk) that the page polls every 1.5s and patches the status badges + summary in place. No more reloading the page to see results land.

4. Visual polish

• Modern CSS: sticky header, sticky table head, zebra/hover rows, colored status badges (green/red/amber).
• A toolbar with a path search box, filter buttons (All / Differences / Pending / Same), and summary chips (total / same / diff / pending counts) that update live.