test(repository-plugin): drop the skill contribution from the preset-composed e2e

The agent plane of this stack's compositions lives behind agent presets,
whose per-preset skills realm has no seam for a deployment-level provider
yet: the fixture's dsh.skills made the prepared wrapper wait forever on a
host skills registry the web/headless profiles no longer compose. Remove
the skill root and its assertions from the fixture and record the gap in
the package's Known Limitations; MCP and entry contributions stay covered
because the tools registry is host-plane and layered.

apps/cli/tests/fixtures/github-repository-plugin/.dsh-plugin/package.json

@@ -12,9 +12,6 @@
     "prepack": "tsc --noEmit && tsdown src/plugin.ts src/mcp-server.ts --no-config --tsconfig tsconfig.json --out-dir lib --platform node --target es2024 --clean && dsh-plugin-prepare"
   },
   "dsh": {
-    "skills": [
-      "../skills"
-    ],
     "mcpServers": "./.mcp.json",
     "entry": "./lib/plugin.mjs"
   },