fix(update): 30-min download timeout + tidier progress number

Follow-up to 56d4875b, same v1.7.0-alpha shipping band.

Backend download timeout bumped from 300s to 1800s (update.rs) with an
explicit 30s connect timeout. git.tx1138.com raw-file throughput can sit
around 70–80 KB/s, which meant OTA downloads were timing out at ~55%
through the 40 MB binary even though the SHA would have matched on a
full pull. 30 min gives ample headroom for the worst LAN-to-VPS link we
actually hit.

Frontend: SystemUpdate.vue now formats downloadPercent with toFixed(2)
via a new computed, so the progress card shows "45.23%" instead of
"45.270894%". Cosmetic only; the underlying ref still tracks raw floats.

Manifest changelog rewritten in user-facing language per the saved
feedback — no file paths, function names, or "root cause" phrasing.

Artifacts refreshed:
  binary   d85a71c5…982f4  40360936
  frontend 8adcdacf…e687f6 76986852

ISO at image-recipe/results/archipelago-installer-unbundled-x86_64.iso
(Apr 20 09:00) carries both fixes for fresh installs.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

core/archipelago/src/update.rs

@@ -157,7 +157,8 @@ pub async fn download_update(data_dir: &Path) -> Result<DownloadProgress> {
         .context("Failed to create staging dir")?;
 
     let client = reqwest::Client::builder()
-        .timeout(std::time::Duration::from_secs(300))
+        .timeout(std::time::Duration::from_secs(1800))
+        .connect_timeout(std::time::Duration::from_secs(30))
         .build()
         .context("Failed to create HTTP client")?;