feat: polish Linux runtime startup and desktop dictation UX

[BLCCoreStudio]

Summary

Real KDE/Wayland validation on 2026-09-06 exposed release-blocking runtime issues and confirmed that the desktop UI needed a focused daily-use pass. This PR hardens those paths and reorganizes the app without changing the established Tauri IPC contract.

Linux/runtime hardening

• Default native ASR builds no longer silently bind to host-wide BLAS/MKL installations; explicit developer overrides remain possible.
• KDE/Wayland startup automatically applies the WebKitGTK DMA-BUF compatibility guard only when the user has not already chosen an override.
• Finite FIR/resampler overshoot is clamped back to normalized PCM bounds before strict ASR validation; NaN/Inf and structurally invalid audio remain rejected.
• Wayland EIS prefers ei_text when the compositor provides it.
• When a compositor provides only a resumed EIS keyboard device, BLCVoice uses the native Wayland clipboard plus the authorized EIS keyboard session to issue the paste shortcut. This fallback has a distinct backend identity (xdgRemoteDesktopEisClipboard) and never activates X11/XWayland, evdev/uinput, root, or another privileged input fallback.

The clipboard fallback intentionally prioritizes semantic UTF-8 delivery on keyboard-only EIS sessions. It may leave the transcript in the user's system clipboard / clipboard history; this side effect must be included in final UX/documentation and runtime validation before release.

Desktop UX

• Main window reorganized into Home / History / Models / Settings / Diagnostics.
• Everyday dictation stays on Home while technical platform backend details move to Diagnostics.
• Shortcut dictation overlay is now a compact left-edge, always-on-top, non-focusable waveform/timer surface.
• Overlay transitions through Preparing → Listening → Transcribing → Sent / recovery states and preserves recoverable transcript text on insertion failure.
• Reduced-motion behavior is retained.

Tracked evidence

• test: establish real-platform compatibility validation matrix #44 contains the exact KDE Plasma 6.7.4 / CachyOS runtime evidence.
• fix(linux): clamp resampler overshoot before ASR validation #65 tracks the ASR normalization failure found in that session.
• fix(wayland): handle KDE EIS sessions without ei_text capability #66 tracks KDE EIS sessions without ei_text.
• feat(desktop): redesign main app and dictation overlay for focused daily use #67 tracks the focused desktop redesign/overlay acceptance criteria.

Merge gate

Keep this PR draft until all CI and desktop bundle jobs pass on one unchanged head and the updated branch is re-tested on the same real KDE/Wayland machine. The real-machine pass must confirm Turkish/UTF-8 text delivery to the intended target, focus preservation, shortcut overlay behavior, history recording, and the actual selected insertion backend.