fix(desktop): replace review emoji with bundled icon

[Antikythera]

What does this PR do?

Hermes Desktop now renders the 💾 Self-improvement review: … system notification with the bundled save Codicon instead of asking Chromium to render the literal floppy-disk emoji.

On Linux/Electron, the small inline system-message typography could render 💾 as a tofu box even when Noto Color Emoji was installed. The message is structured application chrome, so a bundled UI icon is more reliable and visually consistent than depending on host color-emoji fallback.

The original message text is preserved; only the emoji prefix is replaced at render time. CLI and other output paths are unchanged.

Root cause

agent/background_review.py emits a plain-text notification beginning with U+1F4BE (💾). Desktop rendered the complete string through the generic SystemMessage text path. Chromium's Linux color-font fallback did not resolve that codepoint in this compact inline surface, producing the visible missing-glyph box.

This is separate from the private-use Nerd Font fallback in #81013: U+1F4BE is an emoji, not a Nerd Font PUA character. Expanding the Nerd Font fallback cannot correctly solve it.

Implementation

• Recognize the structured self-improvement notification in SystemMessage.
• Strip only its known emoji prefix.
• Render the existing bundled Codicon save glyph alongside the unchanged notification text.
• Leave unrelated system messages on the existing generic path.

Related Issue

Follow-up found while visually validating #81013. It intentionally remains separate because this is a structured-message rendering fix rather than font fallback.

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

How Has This Been Tested?

Check	Result
npm run test:ui -- src/components/assistant-ui/thread/system-message.test.ts	2 passed
npm run typecheck	Passed
npm run lint -- --quiet	Passed
hermes desktop --build-only on a local integration branch containing #81013 and this commit	Passed; Electron 40.10.2 Linux package produced

The regression test verifies that the structured notification is recognized, its text is retained without the emoji prefix, and unrelated system messages are ignored.

Screenshots / Logs

Before

After

Checklist

• My code follows the project's code style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
  • Not applicable: this is an internal rendering correction with no user-facing API or setting.
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have run pytest tests/ -q and all tests pass
  • Not run: the change is isolated to desktop TypeScript/React; the focused UI test, desktop typecheck, lint, and packaged build passed.
• Any dependent changes have been merged and published
  • No dependencies; this PR is independent of fix(desktop): render Nerd Font UI glyphs #81013.

Platform Information

• OS: Bazzite Linux / KDE Plasma / Wayland
• Electron: 40.10.2

[Antikythera]

Packaged-app runtime validation passed on Electron 40.10.2 / Linux:

• Injected a synthetic review.summary event through the renderer's existing gateway event path.
• The compact system message appeared in the active thread.
• DOM verification: containsEmoji: false, hasSaveCodicon: true.
• Rendered text remained Self-improvement review: Visual validation — bundled save icon should appear here.

This exercises the real packaged renderer rather than only the parser unit test.