feat(update-check): suppress popup for releases under 30 min old

GitHub Actions takes ~15 min to build and attach the platform binaries
after a tag is pushed; the latest-release API returns the tag the moment
it's published, so users were getting a popup pointing at a release page
whose asset list was still empty. Parse `published_at` (minimal
YYYY-MM-DDTHH:MM:SSZ → UNIX seconds via days-from-civil, no new deps)
and skip the notification while the release is younger than 30 minutes.
A missing or unparseable timestamp falls through to the old behaviour so
a malformed payload can't permanently silence notifications.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/update_check.rs

@@ -11,6 +11,13 @@ const RELEASES_API: &str =
 pub const RELEASES_PAGE: &str =
     "https://github.com/HakanSeven12/OpenCADStudio/releases/latest";
 
+/// Minimum age before a freshly-published release is offered to the user.
+/// GitHub Actions takes ~15 min to build and attach the platform binaries
+/// after a tag is pushed, so suppressing notifications for the first 30
+/// minutes prevents users from clicking through to a release page whose
+/// asset list is still empty.
+const MIN_RELEASE_AGE_SECS: u64 = 30 * 60;
+
 /// What `check_for_update` reports when a newer release exists.
 #[derive(Debug, Clone)]
 pub struct UpdateInfo {
@@ -48,11 +55,70 @@ fn fetch_latest_if_outdated() -> Option<UpdateInfo> {
     if latest == env!("CARGO_PKG_VERSION") {
         return None;
     }
+    // Suppress the notification until the release is old enough for the
+    // Actions build to have published binaries.
+    if let Some(published) = extract_string_field(&body, "published_at")
+        .as_deref()
+        .and_then(parse_iso8601_utc)
+    {
+        let now = std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .ok()?
+            .as_secs();
+        if now.saturating_sub(published) < MIN_RELEASE_AGE_SECS {
+            return None;
+        }
+    }
     // Release notes are optional; treat missing as empty.
     let notes = extract_string_field(&body, "body").unwrap_or_default();
     Some(UpdateInfo { version: latest, body: notes })
 }
 
+/// Parse a GitHub timestamp like `2026-05-29T12:34:56Z` into UNIX seconds.
+/// Only handles the fixed `YYYY-MM-DDTHH:MM:SSZ` format the GitHub API
+/// emits; returns `None` for anything else.
+fn parse_iso8601_utc(s: &str) -> Option<u64> {
+    let b = s.as_bytes();
+    if b.len() != 20 || b[4] != b'-' || b[7] != b'-' || b[10] != b'T'
+        || b[13] != b':' || b[16] != b':' || b[19] != b'Z'
+    {
+        return None;
+    }
+    let year: i32 = s.get(0..4)?.parse().ok()?;
+    let month: u32 = s.get(5..7)?.parse().ok()?;
+    let day: u32 = s.get(8..10)?.parse().ok()?;
+    let hour: u32 = s.get(11..13)?.parse().ok()?;
+    let minute: u32 = s.get(14..16)?.parse().ok()?;
+    let second: u32 = s.get(17..19)?.parse().ok()?;
+    if !(1..=12).contains(&month)
+        || !(1..=31).contains(&day)
+        || hour >= 24
+        || minute >= 60
+        || second >= 60
+    {
+        return None;
+    }
+    // Howard Hinnant's days_from_civil — converts a proleptic-Gregorian
+    // (Y, M, D) to a count of days since 1970-01-01.
+    let y = if month <= 2 { year - 1 } else { year };
+    let era = y.div_euclid(400);
+    let yoe = (y - era * 400) as u32;
+    let m = month as i32;
+    let d = day as i32;
+    let doy = (153 * (if m > 2 { m - 3 } else { m + 9 }) + 2) / 5 + d - 1;
+    let doe = yoe * 365 + yoe / 4 - yoe / 100 + doy as u32;
+    let days_since_epoch = era as i64 * 146097 + doe as i64 - 719468;
+    if days_since_epoch < 0 {
+        return None;
+    }
+    Some(
+        days_since_epoch as u64 * 86_400
+            + hour as u64 * 3_600
+            + minute as u64 * 60
+            + second as u64,
+    )
+}
+
 /// Minimal extractor for a top-level string field in the releases JSON.
 /// Avoids pulling in `serde_json` for two fields. Handles standard JSON
 /// string escapes (`\"`, `\\`, `\n`, `\r`, `\t`, `\/`) which are all the