fix: eliminate cross-plugin dependencies and modernize plugin.json across marketplace

Rewrites 14 commands across 11 plugins to remove all cross-plugin
subagent_type references (e.g., "unit-testing::test-automator"), which
break when plugins are installed standalone. Each command now uses only
local bundled agents or general-purpose with role context in the prompt.

All rewritten commands follow conductor-style patterns:
- CRITICAL BEHAVIORAL RULES with strong directives
- State files for session tracking and resume support
- Phase checkpoints requiring explicit user approval
- File-based context passing between steps

Also fixes 4 plugin.json files missing version/license fields and adds
plugin.json for dotnet-contribution.

Closes #433

plugins/multi-platform-apps/.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "multi-platform-apps",
-  "version": "1.2.1",
+  "version": "1.3.0",
   "description": "Cross-platform application development coordinating web, iOS, Android, and desktop implementations",
   "author": {
     "name": "Seth Hobson",