fix(tools): coerce stringified argument types to schema expectations (#13350)

[patrickswedish]

Summary

Coerces stringified JSON arrays, objects, booleans, and numbers in tool arguments to match their expected schema types before invoking MCP and built-in tools.

Motivation & Context

Certain models (such as Ollama/Qwen) and serialization pipelines emit tool call arguments where array or object parameters are passed as serialized JSON strings (e.g. {"paths": "[\"file1.jsx\", \"file2.jsx\"]"} or {"dryRun": "false"}). When received by tools (especially MCP servers validating with Zod/JSON Schema), these cause validation failures like:
MCP error -32602: Input validation error: Invalid arguments for tool read_multiple_files: Invalid input: expected array, received string at paths

Changes

• In core/tools/parseArgs.ts, expand coerceArgsToSchema to parse stringified JSON arrays and objects, and coerce boolean and numeric strings to their respective primitives when defined by the schema (including union/anyOf/oneOf constructs).
• In core/tools/callTool.ts, ensure coerceArgsToSchema is run on parsed tool arguments before dispatching to built-in tools as well.
• In core/tools/parseArgs.vitest.ts, add unit tests covering array, object, boolean, number, and union type coercion.

Fixes #13350

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