feat: dark theme onboarding + recording bug fix

[r3dbars]

Summary

• Redesign onboarding to match the floating pill's dark aesthetic (panelCharcoal #1A1A1A, coral accents, white text)
• Simplify UI: remove frosted glass, glow effects, stagger animations, hover scale, gradient overlays, tips carousel, skip link
• Fix recording bug: mic permission now required to proceed (was skippable via "Continue without mic", causing fresh installs to fail)
• Fix pill success state: saved card no longer suppressed during speaker naming

Changes

• 12 files changed, 295 insertions, 683 deletions (~39% net reduction)
• Window: 640x560 (was 720x680), dark chrome, no frosted glass
• BenefitCard: dark reskin, simplified (no hover/glow)
• PermissionsStep: Draft-style simple rows, mic blocks Continue button
• ModelSetupStep: dark cards, coral progress bars, no tips carousel
• PreviewStep: dark transcript card, coral/purple speaker colors on dark
• FloatingPanelController: removed guard blocking saved state during naming
• TranscriptionTaskManager: scheduleStatusReset skips when naming in progress

Test plan

• Fresh install: reset defaults + permissions, launch app, verify dark onboarding appears
• Walk through all 4 steps: Welcome → Preview → Permissions → Model Setup
• Verify mic permission required (Continue disabled until granted)
• Verify recording works after completing onboarding
• Verify pill shows green saved card after transcription completes
• Verify speaker naming tray coexists with saved card

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