Add reusable timeout + abort layer for chat/analyze/dashboard requests

[ApexYash11]

Summary

Implement a standardized cancellation/timeout mechanism for key frontend API calls.

Why

Sequential and fan-out calls can increase latency and degrade UX; docs recommend a reusable abort + timeout layer.

Scope

• Add reusable request cancellation utility used by chat/analyze/dashboard flows.
• Ensure in-flight requests are aborted on route changes or superseding actions.
• Define consistent timeout defaults and per-route overrides.
• Normalize timeout/cancel error handling in UI.

Acceptance Criteria

• Chat, analyze, and dashboard requests support cancellation.
• Timeouts are consistently applied and configurable.
• Users see clear retryable error states on timeout/cancel.

Source

• docs/SITE_FLOW_AND_IMPROVEMENTS.md (Improvement Plan V2 #4)