feat(flash): multi-stage ETA, real-time speed display, download robus…

[Zhang-zu-hao]

Summary

This PR adds multi-stage ETA and real-time speed display to the flash center, and enhances download robustness for SharePoint/OneDrive CDN.

Changes

1. Multi-stage ETA & Speed Display

• Sliding-window algorithm (30s window, 0.5s sampling) for download and extract stages
• 4-stage progress mapping: download 0-50%, verify 50-60%, extract 60-80%, flash 80-100%
• Status label updates every 0.5s (real-time speed/ETA)
• Log updates every 5% (avoid spam)
• Disconnect/resume detection: clears stale samples on cur backwards or >10s gap

2. Download Robustness

• Range request 206 status validation
• Part file short-read detection (got < expected)
• Merged file size verification (actual != declared)
• Retry count 3→5
• SharePoint URL reordering (download=1 first, skip HTML failure)
• print() → _emit_log() (UI-visible messages)
• HEAD request status logging + initial progress emission

3. Bug Fixes

• Fix verify stage progress not showing (shared _last_log_pct variable)
• Fix progress bar regression (flash stage 0% conflicting with extract 80%)
• Fix download scene animation only reaching 50%
• Optimize verify progress_val emission (3M→100 calls)

4. i18n

• New keys: connecting, head_ok, head_failed, eta_calculating, verifying, extracting_with_eta
• Updated: download/extract progress text with {speed} and {eta} placeholders

Files Changed

File	+Add	-Del
flash.py	+52	-17
modules/flash/thread.py	+151	-13
modules/flash/page.py	+96	-18
locales/en/flash.json	+13	-4
locales/zh-CN/flash.json	+13	-4
Total	+325	-56

Test Plan

• Download stage: verify speed/ETA updates every 0.5s, scene animation 0-100%
• Verify stage: verify progress text updates every 10%, no UI lag
• Extract stage: verify speed/ETA display, WSL indeterminate mode
• Flash stage: verify progress 80-100%, no regression
• Disconnect/resume: verify speed/ETA recalculates from new data
• SharePoint: verify download=1 URL tried first, no HTML failure