Add tool calling support

[Aaryan-Kapoor]

Hey Folks,

Related to #535

This PR is to pave the way for adding future MCP tools support. Any recommendations on local vs remote MCP support are welcome too!

In short, this PR:

• Adds OpenAI-compatible tool calling with streaming support and an agentic inference loop (generate → detect tool calls → execute → re-generate, up to 10 rounds)
• Includes DB schema migration for tool definitions, tool call metadata on swipes, and a role field on chat entries
• Ships with two built-in tools (get_current_datetime, calculate with a safe math parser) and a Tool Manager UI for creating/editing/toggling custom tool definitions (more for paving way for MCP support)
• Tool call accumulator handles incremental JSON parsing from SSE streams, including parallel tool calls via index-based accumulation
• Enabled for OpenAI, Open Router, Google AI Studio, and Chat Completions API templates via useTools feature flag

What's included

• Engine: ToolCallAccumulator, ToolExecutor, ToolTypes, built-in tool definitions
• Inference: Agentic loop in chatInferenceStreamWithTools with abort support
• Context/Request builders: Tool message serialization (role: "tool", tool_calls, tool_call_id)
• DB: Migration 0018 - tool_definitions table, role on chat_entries, tool_calls/tool_call_id on chat_swipes
• State: ToolState zustand store with DB-backed CRUD and built-in tool seeding
• UI: Tool Manager screen (list/add/edit/delete/toggle), collapsible tool call indicators and tool result headers in ChatBubble

Known limitations

• OpenAI format only - Claude native tool_use format not yet supported
• Custom tools are definition-only (sent to model but no local execution handler, paves way for MCP)
• Still WIP since this is a huge change, I tested with some basic tool calling working. Contribs are welcome :)

Screenshots

Using GPT-5.4-nano through OpenRouter and the default AI Bot

[Aaryan-Kapoor]

I'd appreciate some feedback on how to handle the UI tool surfacing.

Right now, it just shows up as a user message, which might seem somewhat unsettling and lead to a lot of scrolling!

[Vali-98]

Hey there, thanks for the PR!

Just to let you know, preferably PR's are done to the dev build, as many underlying processes likely have changed. Otherwise, I'll have a proper look at this over the weekend.

[Vali-98]

This extractor should be using the API defined message extractor.

[Vali-98]

I left a few comments on implementation, also there is the matter of how to represent this in the chat. I believe the idea to have tools as separate messages from the tool caller/response is viable, so its just a matter prettifying the UI for it.