doc(redmine6): create v15 page with redmine 6 upgrade notes

docs/Major_releases/v15.md

@@ -0,0 +1,176 @@
+# Version 15
+
+## Most impactful changes
+
+- Redmine upgrade to version 6
+- Hard switch to using Zeitwerk
+  - [File structure and Transition](https://easysoftware.stoplight.io/docs/developer-portal-devs/c5d9cf64cd1e2-file-structure-and-transition)
+  - [Easy Project initialization process](https://easysoftware.stoplight.io/docs/developer-portal-devs/8e822d65a77a2-easy-project-initialization-process)
+
+----
+
+## Redmine 6 Upgrade
+
+This document outlines the most impactful changes and deprecations introduced in the Redmine 6 upgrade. It is intended
+for developers and maintainers who need to understand the implications of these changes on their existing codebases.
+
+### Major Framework Upgrades
+
+- ruby `">= 3.3.1"` → `">= 3.3.7", "< 3.4.0"`
+  - Added upper bound to Ruby version
+- rails `"~> 6.1.7.10"` → `"~> 7.2.2.1"`
+  - Major framework upgrade
+- rack `"~> 2.2.3"` → `"~> 3.1.3"`
+
+### Breaking Changes
+
+#### 1. Aliasing Changes
+
+**Before:**
+
+```ruby
+alias_attribute :host_name, :host
+```
+
+**After:**
+
+```ruby
+alias_method :host_name, :host
+```
+
+- `alias_attribute` is now reserved for actual attributes
+- Use `alias_method` for methods or non-attributes
+
+#### 2. Serialization Changes
+
+**Before:**
+
+```ruby
+serialize :settings, Hash
+serialize :data, Array
+```
+
+**After:**
+
+```ruby
+serialize :settings, type: Hash
+serialize :data, coder: JSON
+```
+
+- Use `type:` parameter instead of direct class
+- For complex objects, use `coder:` parameter with a serializer class
+
+#### 3. ActiveSupport Deprecation Warnings
+
+**Before:**
+
+```ruby
+ActiveSupport::Deprecation.warn("This method is deprecated")
+```
+
+**After:**
+
+```ruby
+ActiveSupport.deprecator.warn("This method is deprecated")
+```
+
+- Changed from class method to instance method via the global deprecator
+
+#### 4. Asset Management
+
+**Before:**
+
+```ruby
+stylesheet_link_tag 'alerts', plugin: 'easy_alerts'
+```
+
+**After:**
+
+```ruby
+stylesheet_link_tag 'alerts'
+```
+
+- Removed plugin specification from asset helpers
+- Asset paths must be properly registered in initializers:
+
+```ruby
+Rails.application.configure do
+  asset_paths = EasyAssets.plugin_asset_paths("plugins/path/to/plugin")
+  config.assets.paths.concat asset_paths
+  config.assets.precompile << "your_asset.css"
+end
+```
+
+#### 5. Default Timezone Access
+
+**Before:**
+
+```ruby
+ActiveRecord::Base.default_timezone == :utc
+```
+
+**After:**
+
+```ruby
+ActiveRecord.default_timezone == :utc
+```
+
+- Default timezone now accessed through ActiveRecord instead of the class
+
+#### 6. Date/Time Formatting Changes
+
+**Before:**
+
+```ruby
+date_value.to_s(:db) # "2023-01-01"
+time_value.to_s(:db) # "2023-01-01 12:34:56"
+```
+
+**After:**
+
+```ruby
+date_value.to_fs(:db) # "2023-01-01"
+time_value.to_fs(:db) # "2023-01-01 12:34:56"
+```
+
+- Changed from `to_s(:db)` to `to_fs(:db)` for date/time formatting
+- This affects all date/time serialization to database format
+- Check any code that formats dates for database queries or display
+
+### Warnings / Deprecations
+
+Deprecated but not yet removed in Rails 7.2.
+
+#### 1. Enum Declaration Changes
+
+**Before:**
+
+```ruby
+enum state: %i[pending active], _prefix: true
+enum status: { running: 0, archived: 1 }, _default: :running
+```
+
+**After:**
+
+```ruby
+enum :state, %i[pending active], prefix: true
+enum :status, { running: 0, archived: 1 }, default: :running
+```
+
+The enum syntax has changed significantly:
+
+- First parameter is now a method name (`:status` instead of `status:`)
+- Removed underscore from some `enum` options (`prefix:`, `suffix:`, `default:` instead of `_prefix:`, `_suffix:`,
+  `_default:`)
+
+### Recommendations for Upgrading
+
+1. **Test thoroughly** - The framework changes are substantial and require extensive testing
+2. **Update dependencies** - Update your gem dependencies to match the new requirements
+3. **Refactor enums and serializers** - These need immediate attention for compatibility
+4. **Check asset loading** - Ensure your assets are properly registered and loaded
+5. **Update deprecation warnings** - Replace deprecated calls with new methods
+6. **Review database migrations** - Ensure compatibility with the new database handling
+7. **Consider Rails 7 compatibility** -
+   Review [Rails 7 upgrade guide](https://guides.rubyonrails.org/v7.2/upgrading_ruby_on_rails.html) for additional
+   changes not covered here

toc.json

@@ -25,14 +25,23 @@
     },
     {
       "type": "item",
-      "title": "File structure and Migration",
-      "uri": "docs/Zeitwerk_support/File-structure-and-migration.md"
+      "title": "File structure and Transition",
+      "uri": "docs/Zeitwerk_support/File-structure-and-transition.md"
     },
     {
       "type": "item",
       "title": "Easy Project initialization process with zeitwerk",
       "uri": "docs/Zeitwerk_support/Easy-Project-Initialization.md"
     },
+    {
+      "type": "divider",
+      "title": "Major Releases"
+    },
+    {
+      "type": "item",
+      "title": "Version 15",
+      "uri": "docs/Major_releases/v15.md"
+    },
     {
       "type": "divider",
       "title": "Hello RYS"