fix: React error #185 in desktop app + marcoreid color + translate caching #4749

Originally written by @ccantynz-alt on GitHub.
Imported from https://github.com/ccantynz-alt/voxlen/pull/52

Summary

• React error #185 fix (desktop app) — "Invalid hook call" can occur when multiple instances of React are loaded into the same bundle. Added resolve.dedupe: ["react", "react-dom"] and explicit alias entries in vite.config.ts to force all imports to the same copy. This is the root cause defence for the recurring error #185 Craig has been seeing in the Dictation panel.
• marcoreid undefined color fixed — marcoreid was never defined in tailwind.config.ts. All elements using text-marcoreid-*, bg-marcoreid-*, border-marcoreid-* were rendering invisible (transparent). Replaced with brand throughout landing page and dashboard.
• Translate API prompt caching — Added anthropic-beta: prompt-caching-2024-07-31 and system block with cache_control: ephemeral to the translate endpoint, matching the grammar endpoint pattern. Reduces latency and cost for repeated translation calls.
• Dashboard stale BYOK copy — "Add an API key to unlock grammar AI" messaging replaced with correct upgrade CTA.

Test plan

• Desktop app: dictation no longer throws React error #185 after rebuild
• Landing dashboard: "Unlock Full Access" card and API key icon show as brand purple (not invisible)
• SEO page nav logo and CTA buttons are now brand purple
• Translation calls benefit from prompt caching on repeated requests

https://claude.ai/code/session_011MFNHeFKrhfuSrEYVgrdyr

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