Remove process manager timeout fallbacks for shell sessions

[akhilsinghcodes]

This change removes the timeout fallback logic from the process manager for shell sessions.

What changed

• Deleted the timeout fallback handling in apps/server/src/processManager.ts
• Simplified shell session lifecycle behavior by relying on the existing session/process management flow instead of additional timeout-based cleanup

Why this matters

• Reduces surprising timeout behavior in shell sessions
• Keeps process management logic more predictable and easier to reason about
• Avoids fallback cleanup paths that could interfere with normal session termination

Scope

• Limited to apps/server/src/processManager.ts
• No UI changes
• No new user-facing features