fix(tui): refine provider failure presentation

[jlongster]

Summary

• render terminal provider failures as concise inline Error: rows and remove duplicate execution-failure toasts
• hide terminal error styling while a retry is scheduled and normalize retry/footer spacing
• extract provider messages from small JSON HTTP error bodies while retaining the full redacted body in diagnostics

Testing

• bun typecheck in packages/ai
• bun test test/executor.test.ts in packages/ai
• bun typecheck in packages/tui
• bun test test/cli/tui/session-rows.test.ts in packages/tui
• OpenCode Drive reproductions for malformed streams, partial disconnects, content filtering, empty responses, output truncation, late stream content, malformed tool input, retries, clean EOF, and HTTP 401

Screenshots

All screenshots were captured from the real V2 TUI with OpenCode Drive.

Malformed stream

Partial output followed by disconnect

Content filter after partial output

Empty successful response

Output-limit truncation

Content after finish

Malformed tool arguments

Provider retry before output

Rate-limit retry row updating in place

Clean EOF: first retry

Clean EOF: accumulated retries

Clean EOF: terminal exhaustion

HTTP 401 with extracted provider message