fix(mobile): break signal report summary sections onto separate lines (port #2317)

[Gilbert09]

Ports #2317 to the mobile app.

Problem

Agent-generated signal report summaries often pack the labelled sections onto a single line, e.g.:

What's happening: text Root cause: more text How to resolve: ...

which renders as one run-on paragraph in MarkdownText.

Change

• Adds formatSignalReportSummaryMarkdown to apps/mobile/src/features/inbox/utils.ts. It inserts blank lines before each bold section header (**What's happening:**, **Root cause:**, **How to resolve:**) and after the header label, so each section and its body render on their own line. Matching is case-insensitive.
• Applies it to the summary passed into MarkdownText in both render sites:
  • the report detail screen (apps/mobile/src/app/inbox/[...id].tsx)
  • the expanded report card in TinderView.tsx
• Adds unit tests covering packed headers, already-separated headers, header-free content, and case-insensitive matching.

Pure presentation formatting in the renderer layer — no main-process or business-logic changes.

Testing

• pnpm --filter mobile test — 202 passed
• pnpm --filter mobile lint — clean

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit a719284.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix(mobile): break signal report summary..." | Re-trigger Greptile}