chore(marketplace): add ourdigital-skills local marketplace + fix README install docs

Add .claude-plugin/marketplace.json defining the ourdigital-skills local directory marketplace: 8 themed skill plugins (core/seo/notion/jamie/notebooklm/gtm/dintel/utils) bundling 66 skills, each path resolving to a root SKILL.md. Passes 'claude plugin validate'.

Fix README install instructions: clarify Quick Install scope (commands + venv + creds, not skills); correct the Claude Code skill symlink target to the skill root (was desktop/, which would not load); fix the Claude Desktop import step.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -139,24 +139,6 @@
         "./custom-skills/90-reference-curator",
         "./custom-skills/92-tui-design-template"
       ]
-    },
-    {
-      "name": "mac-optimizer",
-      "description": "macOS system health toolkit — read-only audits, cleanup, and security checks (mac-doctor, mac-packages, mac-environment, mac-security, mac-cleanup, mac-resources). Command-based plugin.",
-      "source": "./custom-skills/81-mac-optimizer",
-      "strict": false
-    },
-    {
-      "name": "multi-agent-guide",
-      "description": "Multi-agent collaboration framework — agent hierarchies, ownership rules, guardrails, handoff protocols, and CI/CD integration for Claude, Gemini, Codex, and human agents. Command-based plugin.",
-      "source": "./custom-skills/91-multi-agent-guide",
-      "strict": false
-    },
-    {
-      "name": "dintel-bootstrap",
-      "description": "Install and verify D.intelligence custom MCP agents (DTM, D.DA, OurSEO) in settings.json; bootstrap a new machine or diagnose a broken install. Command-based plugin.",
-      "source": "./custom-skills/94-dintel-bootstrap",
-      "strict": false
     }
   ]
 }