ErrorBanner on Timeline Network and RiskMap views

[askmy-stack]

Background

Identified during OSS audit v2 of meridian.

Problem Statement

Inconsistent error UX.

Proposed Solution

Standardize ErrorBanner.

Acceptance Criteria

• Implementation complete
• Tests pass
• Documented in README or docs/

Files / Modules Affected

frontend/src/pages/

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Suggested labels: priority:medium, difficulty:beginner, category:bug
Milestone: v2.0-features
OSS Audit: Master Backlog v2