Normalize Content shapes before message categorization

[DrumRobot]

Problem

categorizeMessage in packages/web/src/lib/utils/message.ts assumes Content is always an array, but Content can also be a string, a single content item, or messages may use a top-level msg field. This causes incorrect categorization for non-array content shapes.

Origin

CodeRabbit review on PR #97 (commit 6d447a6) — identified as out of PR scope.

Proposed Solution

• Add a normalizeContent(content: Content): ContentItem[] helper:
  • string → [{ type: 'text', text: content }]
  • Single ContentItem → [content]
  • ContentItem[] → pass through
  • msg field fallback
• Apply normalization before categorization in categorizeMessage

Acceptance Criteria

• All Content shapes (string, single item, array, msg field) correctly categorized
• Unit tests covering each Content shape variant
• No regression in existing message display