Plugin auto-discovery loads invalid hook type causing /doctor diagnostics failure

## Issue Summary
Claude Code `/doctor` command reports a persistent plugin error related to an invalid hook type, even after removing the problematic plugin from all local configurations.

## Error Details
Plugin: default@skills-library
Error Path: hooks > UserPromptExpansion
Message: Invalid option - 'UserPromptExpansion' is not a valid hook type

Valid hook types: PreToolUse, PostToolUse, PostToolUseFailure, Notification, UserPromptSubmit, SessionStart, SessionEnd, Stop, StopFailure, SubagentStart, SubagentStop, PreCompact, PostCompact, PermissionRequest, PermissionDenied, Setup, TeammateIdle, TaskCreated, TaskCompleted, Elicitation, ElicitationResult, ConfigChange, WorktreeCreate, WorktreeRemove, InstructionsLoaded, CwdChanged, FileChanged

## Root Cause
The fivetran/skills-library plugin (version 1.0.29) has an invalid hook configuration with 'UserPromptExpansion' hook type in hooks.json, which is not recognized as a valid hook type.

## Troubleshooting Attempted
- ✅ Removed plugin from installed_plugins.json
- ✅ Removed plugin from known_marketplaces.json
- ✅ Removed from enabledPlugins in settings.json
- ✅ Added to blocklist.json
- ✅ Cleared local plugin caches
- ✅ Removed invalid UserPromptExpansion hooks from all hooks.json files

## Issue
Despite all these steps, Claude Code auto-discovers and validates the fivetran/skills-library marketplace from GitHub on every startup, reloading the invalid hook configuration before checking if the plugin is disabled/blocklisted.

## Expected Behavior
- Option 1: Validate blocklist/disabled status BEFORE fetching and validating marketplace plugins
- Option 2: Don't report errors for blocklisted/disabled plugins
- Option 3: Remove invalid hook type from upstream plugin

## Environment
- Claude Code: 2.1.89
- Node: v20.10.0
- Platform: macOS

## Impact
Non-critical: Claude Code functionality works fine, but /doctor diagnostics incorrectly shows an error state.