feat: add local agent MCP tools and optional source-grounded AI answers

docs/AI-ANSWERS.md

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+# Optional summaries and questions
+
+searchi's search runs locally with Google EmbeddingGemma 2. You can optionally
+connect an OpenAI-compatible text-generation endpoint to summarize a selected
+document passage or ask a question about it. This does not change the search
+model or require an AI service for ordinary searches.
+
+## Connect your preferred endpoint
+
+In desktop settings, open **Optional AI answers**, enable **summaries and
+questions**, and enter your endpoint's API base URL, model name and API key if
+required. A local server might use
+`http://127.0.0.1:1234/v1`; use the exact URL and model supplied by your provider.
+searchi appends `/chat/completions` to that base URL.
+
+Configuration and the key are kept for the current app session only. They are
+not saved to the search index, settings file or performance reports. Re-enter
+them after restarting the app. There is no default cloud provider.
+
+## Choose what to send
+
+Select a document result with a page, paragraph or text-line source. Open the
+**Summarize or ask** panel and inspect the prepared excerpt. Choose
+**Summarize this passage**, or enter a question and choose **Ask**. Only that explicit action makes a
+request; normal searches and selecting a result do not contact the endpoint.
+
+The request contains the displayed excerpt, your question if present, a generic
+source label and its page/paragraph/line location. searchi does not attach the
+file, send its filename or path, or upload the whole folder. Anything you type
+into the question is sent as entered. A hosted endpoint receives this content;
+a local endpoint keeps it on your machine according to that server's setup.
+
+The excerpt is bounded and can be the beginning of the selected indexed source,
+rather than the exact small search snippet. Read it before sending. Changed or
+deleted source files require reindexing and selecting a current result.
+
+Answers are labeled as model-generated drafts, with source IDs. Read the source
+before relying on an answer: citation checks establish which excerpt was cited,
+not whether every generated claim is correct. Image/audio/video summaries,
+whole-document answers, multiple-result context and conversation history are
+not included in this initial integration.
+
+## Compatible API contract
+
+The adapter sends a non-streaming `POST /chat/completions` request with `model`
+and `messages`. Authentication, when configured, uses a Bearer header. The
+model is instructed to return JSON containing `answer` and `citations` inside
+`choices[0].message.content`. The endpoint must support this shape and the
+chosen model must follow that instruction. Unknown source citations and invalid
+responses produce an error; search remains available.
+
+Requests use timeouts and size limits. Redirects and ambient proxies are
+disabled to keep the configured destination explicit. Endpoint URLs must use
+HTTP or HTTPS and must not contain embedded credentials, query strings or
+fragments. No live hosted provider has been validated by the local fixture
+tests; provider compatibility and answer quality remain release checks.
+
+For the underlying format, see the
+[OpenAI Chat Completions reference](https://developers.openai.com/api/reference/resources/chat/subresources/completions/methods/create).