refactor(ipc): delete legacy chrome-ext:* handlers (Phase 3.6d)
Remove 6 ipcMain.handle blocks for chrome-ext:list, chrome-ext:enable,
chrome-ext:disable, chrome-ext:getStatus, chrome-ext:getUiEntries, and
chrome-ext:openPage. These were superseded by tile:chrome-extensions:*
strict channels in Phase 3.5d. Zero callers remain in app/ or features/.