chore: add update-version.sh to bump version across the project

Prompts for the new version and updates the App csproj Version (single
source of truth), mirrors it into the Android head's
ApplicationDisplayVersion, bumps the Android versionCode, and stubs a
new CHANGELOG.md entry.

update-version.sh

@@ -0,0 +1,67 @@
+#!/usr/bin/env bash
+# Bumps the app version everywhere it's tracked and stubs a CHANGELOG.md entry.
+set -euo pipefail
+
+cd "$(dirname "${BASH_SOURCE[0]}")"
+
+APP_CSPROJ="src/App/PalladiumWallet.App.csproj"
+ANDROID_CSPROJ="src/App.Android/PalladiumWallet.App.Android.csproj"
+CHANGELOG="CHANGELOG.md"
+
+current_version=$(grep -oP '(?<=<Version>)[^<]+(?=</Version>)' "$APP_CSPROJ")
+echo "Current version: $current_version"
+
+read -rp "New version (e.g. 1.0.0): " new_version
+
+if [[ -z "$new_version" ]]; then
+    echo "No version entered, aborting." >&2
+    exit 1
+fi
+
+if ! [[ "$new_version" =~ ^[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
+    echo "Invalid version format: '$new_version' (expected X.Y.Z)." >&2
+    exit 1
+fi
+
+if [[ "$new_version" == "$current_version" ]]; then
+    echo "New version is the same as the current one ($current_version), aborting." >&2
+    exit 1
+fi
+
+# 1. Single source of truth: App csproj <Version>
+sed -i "s|<Version>$current_version</Version>|<Version>$new_version</Version>|" "$APP_CSPROJ"
+
+# 2. Android head: ApplicationDisplayVersion (versionName) must mirror it,
+#    and ApplicationVersion (versionCode) must strictly increase on every
+#    release or users can't update in place.
+current_code=$(grep -oP '(?<=<ApplicationVersion>)[^<]+(?=</ApplicationVersion>)' "$ANDROID_CSPROJ")
+new_code=$((current_code + 1))
+
+sed -i "s|<ApplicationDisplayVersion>$current_version</ApplicationDisplayVersion>|<ApplicationDisplayVersion>$new_version</ApplicationDisplayVersion>|" "$ANDROID_CSPROJ"
+sed -i "s|<ApplicationVersion>$current_code</ApplicationVersion>|<ApplicationVersion>$new_code</ApplicationVersion>|" "$ANDROID_CSPROJ"
+
+# 3. CHANGELOG.md: stub a new entry above the previous top-most one.
+today=$(date +%F)
+if grep -q "^## \[$new_version\]" "$CHANGELOG"; then
+    echo "CHANGELOG.md already has an entry for $new_version, leaving it untouched."
+else
+    awk -v ver="$new_version" -v date="$today" '
+        !done && /^## \[/ {
+            print "## [" ver "] — " date
+            print ""
+            print "TODO: describe the changes in this release."
+            print ""
+            done = 1
+        }
+        { print }
+    ' "$CHANGELOG" > "$CHANGELOG.tmp"
+    mv "$CHANGELOG.tmp" "$CHANGELOG"
+fi
+
+echo
+echo "Updated:"
+echo "  - $APP_CSPROJ: Version $current_version -> $new_version"
+echo "  - $ANDROID_CSPROJ: ApplicationDisplayVersion $current_version -> $new_version, ApplicationVersion (versionCode) $current_code -> $new_code"
+echo "  - $CHANGELOG: stubbed entry for $new_version (fill in the details manually)"
+echo
+echo "Review the diff, fill in the CHANGELOG entry, then commit and tag manually."