Add a branded Speaky menu bar icon

[amrshawqy]

Summary

Replace the generic microphone in the macOS menu bar with a compact, recognizable Speaky mascot icon.

The new icon carries the character's defining pen nib, face, body, arms, and feet while remaining legible at native menu-bar size.

Why

The existing mic.fill symbol communicates audio, but it does not identify which application owns the menu-bar item. It is especially easy to confuse with macOS microphone indicators and other recording utilities.

A stable branded icon makes Speaky immediately recognizable and better matches the existing app icon and in-app character.

Design

• Custom 18 × 18 monochrome vector based on the Speaky mascot.
• Native macOS template rendering for automatic light, dark, selected, and high-contrast appearances.
• Preserved vector representation, with 1× and 2× renditions generated by the asset catalog.
• Stable app identity in the menu bar instead of changing between unrelated generic symbols.
• Explicit Speaky accessibility label.

Recording and transcription state remain visible through the menu content, main window, and notch overlay.

Changes

• Add SpeakyMenuBarIcon.imageset containing the template SVG and asset metadata.
• Use the custom asset in MenuBarExtra.
• Remove the now-unused system-symbol mapping from AppState.

The implementation is limited to two small code edits and one self-contained asset set. It adds no runtime image processing, dependencies, or platform-specific state management.

Validation

• Visually inspected at its native 18-point menu-bar size.
• Verified the compiled asset contains:
  • 18 × 18 1× template rendition
  • 36 × 36 2× template rendition
  • preserved vector representation
• All 45 tests passed across 10 suites.
• Universal Release build succeeded for arm64 and x86_64.
• Strict code-signature verification passed.
• Installed Release product matched the verified build byte-for-byte and launched successfully.

The integration build used the locked dependency versions proposed in #4.