Delay dictation overlay until audio capture is ready

[supfeer]

Description

Starts audio capture before presenting the dictation UI so the beginning of a spoken phrase is retained.

This PR:

• marks capture ready only after the first PCM buffer is accepted
• waits 500 ms of active recording before showing the recording overlay
• plays the configured dictation start sound when the overlay appears
• cancels delayed presentation when capture stops or fails
• keeps app-context capture and AI prewarming on the first-audio boundary

Type of Change

• 🐞 Bug fix
• ✨ New feature
• 💥 Breaking change
• 🧹 Chore
• 📝 Documentation update

Related Issue or Discussion

Related to #477, #236, and #592.

Testing

• Tested on Intel Mac
• Tested on Apple Silicon Mac
• Tested on macOS version: 26.5.2
• Ran linter locally: swiftlint --strict --config .swiftlint.yml Sources
• Ran formatter locally: swiftformat --config .swiftformat Sources
• Ran tests locally:

Additional validation:

• Signed Debug build completed successfully.
• Installed and launched locally with com.FluidApp.local.

Screenshots / Video

• No UI/visual changes; screenshots/video are not applicable.

The existing overlay appearance and layout are unchanged. This PR only changes when the existing overlay and start sound are presented relative to active audio capture.

Notes

• Audio acquisition begins before the 500 ms presentation delay.
• The delay is measured from the first accepted PCM buffer, not from the hotkey event.

[github-actions]

The PR Policy check is blocking this PR because required template information is missing.

Please update the PR description with:

• Related Issue or Discussion
• Screenshots / Video

Visual files detected:

• Sources/Fluid/ContentView.swift
• Sources/Fluid/Services/MenuBarManager.swift

Screenshots or video are required for UI, UX, settings, onboarding, overlay, menu bar, or visual behavior changes. If this PR has no visual changes, check the no-visual-change box in the template.

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