Name the silent microphone on the pill

[alexkroman]

Problem

When the mic delivers only silence, Blurt's liveness gate fails closed (correctly). The pill said only ERROR, and the reason, "The microphone didn't start.", was only in a hover tooltip. Nothing on screen pointed at the actual cause, so it looked like a Blurt bug.

Seen in the field: the default input was an Audio MIDI Setup aggregate of a Focusrite Scarlett and BlackHole. With the Scarlett unplugged, only BlackHole was left in the aggregate, delivering -758 dBFS on every channel. Seven presses in a row failed, all with the same unexplained error.

Change

The pill now names the device: AGGREGATE DEVICE ISN'T SENDING ANY AUDIO.

Engine

• MicCaptureError.inputNeverDelivered(deviceName:). The name is looked up (AudioInputDevices.inputName(pinnedUID:)) only on the failure path, so a successful press pays nothing extra.
• BlurtError drops the "Audio capture failed:" prefix for MicCaptureError, whose messages are already user-facing sentences. Other capture errors keep it.
• New OverlayUIState.inputSilent(deviceName:), which owns the wording:
  • pillNotice (subject + predicate) for the pill
  • the sentence form for VoiceOver and hover
  • a 3 s dwell
• Every other failure still maps to .error and keeps the compact ERROR pill.

Overlay (Mac shell)

• For this notice only, the panel widens to fit the text. It stays centred, is capped at 340 pt, and is clamped onto the screen. Afterwards it returns to the saved drag position, which is still stored in standard-width coordinates.
• Long device names truncate in the middle. "isn't sending any audio" never truncates, and the text never shrinks.
• The swap to the wide pill happens under a panel fade, not the usual content cross-fade. Two reasons:
  • The window resizes a frame before SwiftUI redraws.
  • withTransaction doesn't reach this view, because the @Observable bridge is applied in a later update. A flag on the bridge carries "don't cross-fade this change" instead.
• NSHostingView.sizingOptions = [] so the controller alone sizes the panel.

Verification

• swift test: 774 tests pass, including new ones for the message, pillNotice/pillText, the sentence form, and "only this notice writes on the pill".
• swift-format lint --strict, swiftlint --strict and check-invariants.sh pass. The Debug app and dev-build.sh both build.
• On hardware: Blurt Dev pinned to a silent BlackHole input. Burst screenshots show "Connecting" changing straight to the centred wide pill with no glitch frames. A throwaway build with the cap cut to 200 pt confirmed truncation: "…ISN'T SENDING ANY AUDIO" stays whole at full size.
• swift6-concurrency-reviewer: no issues; its suggested comment on payload-blind error equality is added.
• macos-hig-reviewer: its truncation, shrink and edge-clamp findings are fixed.
• Not changed: the reviewer suggested 10–11 pt sentence case for this notice instead of the pill's 9 pt status-line capitals. That's a design call I left out of this PR.

Not in this PR

The log line still says "input liveness unconfirmed … — proceeding" even though the press fails there. It's a one-word follow-up.

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