fix: align error toast color with brand

[CypherPoet]

Fixes #593

Description

This PR changes error toasts to use Bitkit's brand color (#FF4400) in place of the red accent (#E95164), following the design direction in #593. The design prototype renders all of its failure toasts in the brand color, and per John it is close enough to the red accent that using one color is the cleaner choice. Error and warning toasts now share the brand accent.

Linked Issues/Tasks

Fixes #593 (spun out of the color-alignment review on #592)

Screenshot / Video

QA Notes

Manual Tests

• 1. Send → Paste Invoice with invalid clipboard text: Unable To Read QR toast renders with the brand orange title and tint, not crimson.
• 2. regression: Settings → Advanced → Address Viewer → long-press an address: Copied To Clipboard toast is still green.

Automated Checks

N/A (one-line palette change; verified visually on the iOS simulator)

[greptile-apps]

Greptile Summary

This PR aligns error toast colors with the Bitkit brand by swapping .redAccent for .brandAccent in the accentColor switch inside ToastView, matching the design prototype direction described in #593.

• ToastView.swift: Single-line change — .error case now returns .brandAccent instead of .redAccent, making it visually identical to .warning toasts.
• changelog.d/next/594.changed.md: New changelog fragment accurately captures the intent of the change.

Confidence Score: 5/5

Safe to merge — a single color constant swap with no logic, data, or behavioral changes beyond the visual appearance of error toasts.

The change touches exactly one return value in a pure color-mapping switch. It cannot affect dismissal logic, auto-hide behavior, or any other toast functionality. The changelog entry is accurate and the QA steps in the PR description cover both the changed path and a key regression case.

No files require special attention.

Important Files Changed

Filename	Overview
Bitkit/Components/ToastView.swift	One-line palette change: .error toast accent color updated from .redAccent to .brandAccent, matching .warning; no logic affected.
changelog.d/next/594.changed.md	New changelog fragment describing the error toast color change; content is accurate and clear.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[toast.type] --> B{switch accentColor}
    B -->|.success| C[.greenAccent]
    B -->|.info| D[.blueAccent]
    B -->|.lightning| E[.purpleAccent]
    B -->|.warning| F[.brandAccent]
    B -->|.error| G[.brandAccent ← was .redAccent]
    F & G --> H[same brand orange]

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