refactor: replace ban-types Function with real call signatures

[pedrofrxncx]

Two spots in the codebase type a callback as the bare Function type, which the repo's ban-types oxlint rule flags (a warn-level rule, not CI-enforced, so it accumulates as un-caught debt) — Function accepts any arity/argument types, so a caller can pass the wrong shape and only find out at runtime.

1. packages/mcp-utils/src/sandbox/run-code.ts: executePendingJobs on QuickJSRuntime already has a real exported signature, (maxJobsToExecute?: number | void) => ExecutePendingJobsResult, from quickjs-emscripten-core's own .d.ts. Typed the inline ctx.runtime param against that instead of Function.
2. apps/api/src/harnesses/decopilot/built-in-tools/index.ts: instrumentBuiltIns casts each AI-SDK tool's execute to read it off before wrapping. Both call sites (originalExecute.call(t, input, options)) always pass exactly two arguments, so the cast is now (input: unknown, options: unknown) => unknown instead of Function.

Why a maintainer wants this: a real signature is what bunx tsc --noEmit can actually check a call against; Function is a no-op for that in both places.

Behavior-preserving — same runtime code, only annotations changed. No test needed (pure type-level change); a reviewer confirms with:

cd packages/mcp-utils && bunx tsc --noEmit
cd apps/api && bunx tsc --noEmit
bunx oxlint packages/mcp-utils/src/sandbox/run-code.ts apps/api/src/harnesses/decopilot/built-in-tools/index.ts

Locally ran: bun run fmt, bunx tsc --noEmit in both packages/mcp-utils and apps/api (both clean), and bunx oxlint on both touched files (0 warnings/errors). Full CI validates the rest.

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Summary by cubic

Replaces bare Function annotations with real call signatures in two spots so tsc can actually check callback shapes instead of accepting anything at compile time.

• In packages/mcp-utils/src/sandbox/run-code.ts, executePendingJobs now types the runtime callback as (maxJobsToExecute?: number) => ExecutePendingJobsResult, matching quickjs-emscripten-core's exported signature.
• In apps/api/src/harnesses/decopilot/built-in-tools/index.ts, the execute cast is now (input: unknown, options: unknown) => unknown, matching the two call sites that pass exactly those arguments.

Behavior is unchanged; this is a pure type-level refactor, so no tests or runtime effects. Verify with bunx tsc --noEmit in packages/mcp-utils and apps/api, plus bunx oxlint on both touched files.

^{Written for commit 529fefa. Summary will update on new commits.}