fix: cross-platform WebGL/audio UX, packaging metadata, and docs test count (2577)

[CaYatur]

Summary

Cross-platform fixes for WebGL fallback, visualizer initialization, audio capture status and diagnostics, packaging metadata, and the documentation test count (2577). Linux was the primary verification environment; platform-specific audio copy now distinguishes Windows, macOS, and Linux.

Changes

• K1 — WebGL gradient fallback (cross-platform): If the gradient WebGL constructor fails, use a silent 2D solid-color fallback, guard the null context, and surface a non-blocking admin/scene notice plus sv-gradient-webgl-fallback. This applies wherever WebGL is unavailable, not only on Linux.
• M1 — Platform-aware audio diagnostics: NO_DEVICES, ACCESS_DENIED, and timeout guidance now use the appropriate Windows, macOS, or Linux PulseAudio/PipeWire instructions.
• M2 — Visualizer draw gate (cross-platform): draw is no longer gated on audio.ready, allowing MilkDrop/Studio/WebGL initialization and rendering with idle or zeroed audio buffers; it still clears safely when no audio object exists.
• Audio status (cross-platform): Turkish and English status consistently report Yakalanıyor: … / Capturing: … with the resolved source label, without allowing device refreshes to overwrite an active-capture state.
• M3 — Packaging metadata: package.json now lists Linux alongside Windows and macOS.
• Electron/smoke compatibility: Update console-message handling for the current Electron event shape and avoid false texture-share failures on unsupported platforms.
• Docs: Update README.md, README.tr.md, and ROADMAP.md test counts to 2577.
• Tests: Add WebGL fallback/M2 regression coverage and platform-specific native-audio and packaging assertions.

Verification

• Targeted: node --test tests/layers-webgl-fallback.test.js tests/native-audio-runner.test.js tests/platform-packaging.test.js → 38 passed
• Linux was used for the primary verification; the cross-platform code paths and platform-specific message branches are covered by tests where applicable.