feat(web): improve agent performance, MCP tools, and much more

[brendan-kellam]

This PR is effectively a re-work of the tools we ship in our MCP server & ask agent. There are many details & changes in this PR, most of which are covered in the changelog. In terms of the impact of this PR:

• Tool outputs have been optimized to minimize the amount of tokens. Impact: thread will use significantly less tokens (~95% reduction in the brief tests I ran)
• Changed search_code to look like grep (also renamed it to grep). Agents have a much easier time using understanding and using the grep syntax over our custom search syntax. Impact: The agent will be able to search and find things much more effectively and efficiently.
• Added groupByRepo to grep (prev. search_code) to allow agents to get compact responses that aggregate search results by repo. Impact: Agents are able to get a high-level overview of what terms exist in which repositories without blowing up their context window. This is really helpful when searching over a large number of repos since it gives the agent the ability to narrow down it's search to only repositories that are relevant.
• Added glob, and listTree tools. Impact: the agent has additional mechanisms for exploring repositories.
• Removed the constraint on the search scope selector that required at least one repository to be selected. Impact: it's much easier to search across everything.

Fixes #911
Fixes #848

Summary

• Introduces a shared ToolDefinition<TName, TShape, TMetadata> abstraction in features/tools/ with a unified execute(input, context) signature and ToolResult<TMetadata> return shape
• All tools (read_file, list_commits, list_repos, search_code, find_symbol_references, find_symbol_definitions, list_tree) are now defined once and registered with both the Vercel AI agent and the MCP server via toVercelAITool and registerMcpTool adapters
• Adapters inject call-site context (source: 'agent' or source: 'mcp') into every tool execution
• isReadOnly and isIdempotent hints are declared on each tool definition and forwarded to MCP annotations via registerMcpTool
• Tool names normalized to snake_case throughout; toolNames constant eliminated in favour of xDefinition.name
• Added list_tree tool to the Vercel AI agent with a UI component in the details card
• Tool metadata fields normalized (repository → repo); webUrl added to search_code output
• Shared logger.ts for tools; debug logging added to all tools using consistent snake_case names
• Tool descriptions updated with usage guidance (retry on repo-not-found errors, list_repos discovery, webUrl linking)
• Copy-to-clipboard button moved into ToolHeader so all tool components get it for free