refactor(files): files page rework with unified gcode loader, metadata page and USB mount fixes

[gmmcosta15]

Description

• Feature
• Bug fix
• Code refactor
• Documentation

Rework of the files page and its data layer, plus the USB mount path that fed it. 30 commits, 32 files, +3491/-1790.

Files page and metadata

• Reconcile-based files page with single-owner metadata and LRU caches, filesPage.py cut roughly in half.
• New shared gcode_loader unifying gcode metadata and thumbnail parsing, table-driven, with a tail RAM cap.
• New metadataPage with categorized 2x2 cards, units, key-left/value-right rows and touch scroll.
• New themed blocks_combobox for material filtering, opaque popup, matched row font.
• Sortable file list including Print Time by estimated_time, new sort_asc/sort_desc icons.
• Info button in the confirm box and print page opens the metadata detail view.
• Last print duration from job history, completed jobs only, chamber temp dropped.

Fixes

• USB symlink was created under a literal ~ because the cfg value was never expanded, so no drive ever appeared and stale links could not be reaped.
• device_mounted / device_unmounted were declared and wired but never emitted, so drives showed on unplug instead of insert.
• Dead symlinks looked live because os.path.exists follows the link, now os.path.ismount(os.path.realpath(...)).
• Dir listings now resolve against each response's own request dir, fixing wrong-folder contents.
• USB preload race, O(N^2) list rebuild, expand-arrow double-tap, late thumbnail repaint, list model crash.
• Nozzle temp key with PLA-type fallback, RTL-flipped metadata rows, batched filelist entries.

Motivation

The files page mixed data ownership, parsing and presentation, which made USB behaviour unfixable in place. The USB layer was separately broken end to end: the symlink was never created on any printer, so the UI had nothing to show and a manual refresh was the only workaround.

Tests

• 75 new unit tests in 7 files covering udisks symlink liveness, entry delegate, moonrest headers, thumbnail loader, files data, files page and metadata page.