Refactor: improve file system robustness and path safety

[RinZ27]

Refactored file handling logic to enhance the agent's robustness and protect against malformed inputs.

Specific changes:

• Ported the ticker sanitization logic to the new cache.ts utility to prevent Path Traversal vulnerabilities in the updated architecture.
• Cleaned up .env interactions in env.ts by removing redundant checks, which effectively eliminates potential TOCTOU race conditions.
• Shifted the I/O strategy toward direct exception handling instead of pre-operation state checks, making the overall system more resilient during concurrent operations.

I noticed these edge cases during a quick audit and realized they could impact the agent's reliability when dealing with unconventional tool arguments. Using alphanumeric filters for tickers seemed like the most straightforward way to ensure path integrity without adding complexity.

[virattt]

@RinZ27 should the base branch here be main?

[RinZ27]

@virattt Agreed, switching the base branch to main ensures these path safety improvements land everywhere. While targeting the multi-model logic earlier felt like the priority, keeping the core robust on main is definitely the right call. Just updated the base branch, let me know if this works for you.