Workflow chores: publish Flutter builds & bump alpha versions (#599)

* Add debug mobile artifacts to GitHub releases

- Modify flutter-build.yml to trigger on version tags (v*) and support
  workflow_call for use by other workflows
- Add mobile job to publish.yml that calls flutter-build workflow
- Add release job that creates GitHub release with debug APK and
  unsigned iOS build when a version tag is pushed
- Auto-detect debug vs release APK and name appropriately
- Mark alpha/beta/rc versions as pre-releases

* Add automatic alpha version bump after release

When an alpha tag (e.g., v0.6.7-alpha.3) is published and the Docker
image is built, automatically bump the alpha number in version.rb
(e.g., alpha.3 -> alpha.4) and push to main branch.

* Fix APK copying to include both debug and release builds

Change if/elif to separate if statements so both app-debug.apk and
app-release.apk are copied to release assets when both exist.

* Rename artifact names in publish workflow

Signed-off-by: Juan José Mata <juanjo.mata@gmail.com>

* Revert rename of artifact names

Signed-off-by: Juan José Mata <juanjo.mata@gmail.com>

* Enhance version bump process in publish.yml

Refactor version bump script to ensure version file exists and improve error handling.

Signed-off-by: Juan José Mata <juanjo.mata@gmail.com>

---------

Signed-off-by: Juan José Mata <juanjo.mata@gmail.com>
Co-authored-by: Claude <noreply@anthropic.com>

.github/workflows/flutter-build.yml

@@ -4,6 +4,8 @@ on:
   push:
     branches:
       - main
+    tags:
+      - 'v*'
     paths:
       - 'mobile/lib/**'
       - 'mobile/android/**'
@@ -17,6 +19,7 @@ on:
       - 'mobile/ios/**'
       - 'mobile/pubspec.yaml'
       - '.github/workflows/flutter-build.yml'
+  workflow_call:
   workflow_dispatch:
 
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