Polish Refstream and expose account deletion

[TeoSlayer]

Summary

• promote the existing safe account-deletion flow into a visible danger section
• label Refstream as an unstable alpha when selected in public and signed-in sessions
• replace translucent Refstream app chrome with an opaque terminal-native theme
• update the changelog and renderer documentation

Verification

• npm run check (94 tests plus integration checks)
• npm test in app/ (841 passed, 3 skipped)
• app and root typechecks
• public and app production builds
• desktop visual regression fixture for Refstream controls, ANSI contrast, and continuous canvas