feat(plugins): add export and share contextual actions to plugin catalog (#605)

[annukumar123]

Summary

Adds contextual export and share capabilities to individual plugin items in the PluginsPanel catalog component (#605).

Changes Made

• Share Action (PluginsPanel.jsx):
  • Implemented share link generation targeting the specific plugin ID (?plugin=${plugin.id}).
  • Added clipboard fallback and temporary UI banner notification ("Copied share link for [Plugin]!").
• Export Action (PluginsPanel.jsx):
  • Added JSON configuration file export trigger via DOM anchor download.
  • Generates downloadable ${plugin.id}-config.json containing plugin metadata.
• Contextual Menu (PluginsPanel.jsx):
  • Integrated dropdown options menu (⋮) for each plugin chip.
  • Added event listeners for outside clicks and Escape key to close open menus cleanly.
• Unit Testing (PluginsPanel.test.jsx):
  • Created standalone test suite validating clipboard copy functionality and anchor element download triggers.

Verification

• Ran Vitest suite: npx vitest run src/components/PluginsPanel.test.jsx
• Result: 4 passed (100%)

Fixes #605

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