fix: preserve int64 file IDs

[victor0602]

What changed

• Stop coercing file IDs through JavaScript Number in CLI and FileSDK deletion paths.
• Normalize positive int64 IDs as decimal strings and reject invalid or unsafe numeric inputs locally.
• Support string, safe integer number, and bigint inputs in FileSDK.
• Add coverage for IDs above Number.MAX_SAFE_INTEGER and the int64 boundary.

Why

JavaScript Number cannot precisely represent the complete int64 range documented by the file deletion API.

Impact

Large file IDs are sent without precision loss, while existing safe numeric callers remain supported.

Checks

• bun test — 453 passed
• bun run typecheck
• bun run lint — no errors; one pre-existing test warning
• git diff --check

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