[Chore] (android-plugin): make versionCode monotonic within a month

major*100 + minor collides for multiple releases in the same month, and
Android refuses to install a package whose versionCode is not strictly
greater than the installed one. Encode as year*1_000_000 + month*10_000 +
monthly-revision (commits since the month start), so every build upgrades
cleanly; the month weight dwarfs the per-month reset on rollover.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

android-plugin/app/build.gradle

@@ -46,6 +46,21 @@ def mobileGlGitShortHash = {
         'nogit'
     }
 }()
+// Monthly revision: commits reachable from HEAD since the start of the
+// version's month. Multiple releases in one month (calendar versioning ships
+// several per month) each get a strictly larger versionCode; a new month
+// bumps the minor and dwarfs any reset via the *10000 weight.
+def mobileGlMonthlyRevision = {
+    try {
+        def since = String.format('%d-%02d-01T00:00:00', 2000 + mobileGlVersionMajor, mobileGlVersionMinor)
+        def proc = ['git', 'rev-list', '--count', "--since=${since}", 'HEAD'].execute(null, rootDir)
+        proc.waitFor()
+        def n = proc.in.text.trim()
+        (proc.exitValue() == 0 && n) ? n.toInteger() : 0
+    } catch (Exception ignored) {
+        0
+    }
+}()
 
 android {
     namespace 'top.mobilegl.plugin'
@@ -55,7 +70,11 @@ android {
     defaultConfig {
         minSdk 26
         targetSdk 34
-        versionCode mobileGlVersionMajor * 100 + mobileGlVersionMinor
+        // year*1_000_000 + month*10_000 + monthly revision keeps versionCode
+        // strictly increasing across releases (monotonic within a month and
+        // across month/year rollovers), so every build is an installable
+        // upgrade. Max ~99_129999, well under Android's 2_100_000_000 ceiling.
+        versionCode mobileGlVersionMajor * 1000000 + mobileGlVersionMinor * 10000 + mobileGlMonthlyRevision
         versionName String.format('%d.%02d.%s', mobileGlVersionMajor, mobileGlVersionMinor, mobileGlGitShortHash)
 
         ndk {