Combine browser and auth-wait prompts in auth flow

[Copilot]

The auth login flow had two separate sequential prompts ("Open browser? [Y/n]" then "Waiting for authentication…"), and URLs could be truncated when the terminal was narrower than the URL length.

Auth flow redesign (internal/auth/login.go, internal/ui/app.go)

• Replaces the two-prompt sequence with a single screen showing numbered steps (open link → verify code) plus a unified ENTER wait prompt
• hardWrap now operates on []rune slices — fixes mid-character splits for multi-byte/emoji URLs
• findURL searches from the end of the line buffer to return the most recent URL

Clipboard improvements (internal/ui/app.go)

• Clipboard copy moved to an async Bubble Tea command (clipboardCmd) so Update() is never blocked; copiedFlash is set only on clipboardResultMsg{ok: true}
• Added Wayland support (wl-copy, prioritized when XDG_SESSION_TYPE=wayland or WAYLAND_DISPLAY is set) and Windows support (cmd /c clip)
• Pending input key handling now evaluated before the global c shortcut, so an input option keyed "c" correctly takes priority

Tests

• Unit tests for async clipboard dispatch, clipboardResultMsg flash states, UTF-8 hardWrap, and c-key priority edge case
• Integration tests updated to match the single-prompt flow

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