fix(plugins): hooks.json must be {"hooks": {}} not []; add plugin-validate CI
The empty-array hooks.json in private-equity, financial-analysis,
equity-research and wealth-management caused those plugins to fail to
load ("Hook load failed: expected object, received array"). Replace [] with
the minimal valid {"hooks": {}} object in all four.
Add a plugin-validate workflow that runs the official `claude plugin
validate` over the marketplace manifest and every plugin on each PR and
push, so a malformed manifest fails CI instead of reaching users. The
CLI is installed from the official binary channel and cached, keyed on a
pinned version, so a warm cache skips the download entirely.
Omar Mihilmy
9affc6e683