Remove no-explicit-any suppression from McpHandler.tool

The Obsidian plugin review rejects any disabling of
@typescript-eslint/no-explicit-any. Rather than suppressing the rule,
make the private tool() helper generic over the callback's argument
type: every registration site already annotates its callback parameter
explicitly (e.g. `async ({ path }: { path?: string })`), so inference
flows from the callback and the schema parameter can be typed as a
plain Record of Zod validators. The schema is deliberately not linked
to the argument type via z.objectOutputType to avoid the SDK type
evaluation blowup documented on MinimalMcpServer.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>