feat(pro): add plugin marketplace with catalog, install, and update support
Marketplace backend (agor-pro/src/marketplace.rs): fetch catalog from
GitHub, download+verify+extract plugins, install/uninstall/update with
SHA-256 checksum verification and path traversal protection. 6 Tauri
plugin commands.
PluginMarketplace.svelte: Browse/Installed tabs, search, plugin cards
with permission badges, one-click install/uninstall/update.
Plugin catalog repo: agents-orchestrator/agor-plugins (3 seed plugins).
Plugin scaffolding: scripts/plugin-init.sh.
7 marketplace vitest tests, 3 Rust tests.