chore: remove obsolete .claude-plugin directory

GSD uses npm installation (npx get-shit-done-cc) only.
The plugin.json also referenced non-existent auto.md.

Closes #49

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -1,17 +0,0 @@
-{
-  "name": "get-shit-done",
-  "owner": {
-    "name": "glittercowboy"
-  },
-  "plugins": [
-    {
-      "name": "get-shit-done",
-      "description": "A meta-prompting, context engineering and spec-driven development system for Claude Code by TÂCHES.",
-      "author": {
-        "name": "TÂCHES"
-      },
-      "version": "1.3.20",
-      "source": "./"
-    }
-  ]
-}

.claude-plugin/plugin.json

@@ -1,31 +0,0 @@
-{
-  "name": "get-shit-done",
-  "version": "1.3.20",
-  "description": "A meta-prompting, context engineering and spec-driven development system for Claude Code by TÂCHES.",
-  "author": {
-    "name": "TÂCHES"
-  },
-  "license": "MIT",
-  "repository": "https://github.com/glittercowboy/get-shit-done",
-  "commands": [
-    "./commands/gsd/new-project.md",
-    "./commands/gsd/create-roadmap.md",
-    "./commands/gsd/map-codebase.md",
-    "./commands/gsd/plan-phase.md",
-    "./commands/gsd/execute-plan.md",
-    "./commands/gsd/progress.md",
-    "./commands/gsd/complete-milestone.md",
-    "./commands/gsd/discuss-milestone.md",
-    "./commands/gsd/new-milestone.md",
-    "./commands/gsd/add-phase.md",
-    "./commands/gsd/insert-phase.md",
-    "./commands/gsd/discuss-phase.md",
-    "./commands/gsd/research-phase.md",
-    "./commands/gsd/list-phase-assumptions.md",
-    "./commands/gsd/pause-work.md",
-    "./commands/gsd/resume-work.md",
-    "./commands/gsd/consider-issues.md",
-    "./commands/gsd/help.md",
-    "./commands/gsd/auto.md"
-  ]
-}