fix(tools): bound memory forget requests

[abhinavkr26104]

Summary

• Add a 30-second default timeout to the shared DELETE /v4/memories helper.
• Allow callers to provide an AbortSignal for cancellation.
• Add regression coverage for both the default timeout signal and caller-provided signals.

This prevents AI SDK and OpenAI tool memory-forget calls from remaining pending indefinitely when the API or network stalls.

Fixes #1452

Testing

• bunx vitest run packages/tools/src/tool-operations.test.ts — 14 passed
• bun run --cwd packages/tools build — passed
• bunx biome check packages/tools/src/shared/forget-memory.ts packages/tools/src/tool-operations.test.ts — passed

The full tools test command still has two pre-existing failures requiring SUPERMEMORY_API_KEY and a missing test/claude-memory module. Package type-checking also reports existing dependency/test errors unrelated to this change.

Checklist

• Minimal targeted change
• Tests added for default timeout and explicit cancellation
• No unrelated files included