feat: discover MCP tools via protocol probing for approval pill

When MCP server configs declare wildcard tools (empty tools array),
the Copilot SDK has no API to list individual tool names. Add direct
MCP protocol probing using @modelcontextprotocol/sdk to discover
available tools from each accepted server.

- Add McpToolProber service supporting stdio/SSE/HTTP transports
- Probe accepted MCP servers on project load, acceptance, and rescan
- Store probed tools on DiscoveredMcpServer and McpServerDefinition
- Use probed tools in listApprovalToolDefinitions when declared tools
  are empty, so the approval pill shows individual tool toggles
- Remove unused isMcpServerApprovalKey helper
- Fix effectiveAutoApprovedCount Math.max workaround in ChatPane
- Add comprehensive tests for probed tool behavior
- Update ARCHITECTURE.md tooling integration section

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

ARCHITECTURE.md

@@ -275,6 +275,7 @@ Tooling is deliberately split into two levels:
 
 - **dynamic runtime tools** reported by the Copilot CLI, with a fallback catalog for startup/offline cases
 - **global definitions** for MCP servers and LSP profiles
+- **MCP tool discovery** — when MCP server configs declare wildcard tools (empty `tools` array), the main process probes each server directly via the MCP protocol `tools/list` method to discover available tools, using the same auth credentials Aryx manages for OAuth-protected servers
 - **pattern defaults** where tool-call approval is enabled by default, plus which known runtime tools can bypass manual approval
 - **per-session overrides** for both tool enablement and tool auto-approval