Wasted search-term spend finder

Read https://www.sellermate.ai/api-docs first. It documents the SellerMate Public API: REST over HTTPS, X-API-Key auth, and every tool with its parameters is on that page. Every tool is POST https://api.sellermate.ai/public/v1/tools/{name} with a JSON body.

Build me a script that finds wasted search-term spend for one Amazon account.

It should:
- Pull the last 30 days of search terms with get_search_term_performance, walking every page
- Keep terms with at least [10] clicks and zero orders, or ACoS above [80]%
- Write them to wasted-terms.csv with campaign, ad group, search term, clicks, spend, orders, ACoS
- Print the total spend on that list
- With an --apply flag, add the zero-order terms as negative exact keywords in their ad group using add_negative_keywords, 50 per call, and print what was added. Without the flag, change nothing.

Let me pick the account from get_user_context, or take it as --account.

Rules:
- My key is in the SELLERMATE_API_KEY environment variable. Send it as the X-API-Key header. Never hard-code it or log it.
- Call get_user_context first and use the accounts it returns. Don't invent account ids.
- Report tools are paginated (page, page_size up to 500, pagination.hasMore). Walk every page.
- On a 429, wait for the Retry-After header and retry. On a 401 or 403, stop and tell me.
- Show me the plan and the code before running anything that writes.

Stack: Python 3 with requests. Keep it to one file.