fix(release): support fix releases on top of a weekly one

`v2026.40.1` matched neither the weekly pattern nor plain semver (2026 is
past the MSI major limit), so a fix release could not be built. Weekly
tags now take an optional patch: Cargo 2026.40.1, MSI 26.40.1, display
2026.40.1 (week zero-padded, as build.rs and the update check expect).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

build.rs

@@ -6,10 +6,13 @@ use std::path::Path;
 fn main() {
     let version = std::env::var("CARGO_PKG_VERSION").expect("Cargo package version");
     let parts: Vec<&str> = version.split('.').collect();
-    let app_version = if parts.len() == 3 && parts[0].len() == 4
-        && parts[0].starts_with("20") && parts[2] == "0"
-    {
-        format!("{}.{:02}", parts[0], parts[1].parse::<u32>().expect("week number"))
+    let app_version = if parts.len() == 3 && parts[0].len() == 4 && parts[0].starts_with("20") {
+        let week = parts[1].parse::<u32>().expect("week number");
+        if parts[2] == "0" {
+            format!("{}.{week:02}", parts[0])
+        } else {
+            format!("{}.{week:02}.{}", parts[0], parts[2])
+        }
     } else {
         version.clone()
     };