Revert to Anthropic completions endpoint to avoid rate limiting issues with copilot

Improvements

• CoreFix frontmatter adding newlines causing invalid model IDs
• CoreEnsure that Kimi doesn't have fake variants available
• CoreAdd sequential numbering for forked session titles@ariane-emory
• TerminalAdd additional timeout race condition guards
• TerminalGuard destroyed input field in timeout callback
• TerminalInclude cache tokens in CLI statistics@bold84