feat: smart auto-poke with guardrail, error detection, /poke status

[alecuba16]

Changes

Independent from input flow

• Auto-poke submits directly to model via Message::auto_poke() + run_query_loop
• Does NOT touch prompt_input.text — user can keep typing while poke runs

Smart features

• Guardrail circuit breaker — stops after 3 consecutive provider refusals
• Non-retryable error detection — stops on billing/auth/payload-size errors
• /poke on|off|status — subcommand variants with detailed status display (pokes used, budget left, incomplete todos, guardrail stops, blocked status)
• User-visible messages — "X incomplete todos. Poking. /poke off to stop." / "All todos done." / "Provider refused N turns — stopping."
• Distinct dim yellow color for auto-poke messages in transcript
• Shorter prompt — "X incomplete todos. Continue." instead of verbose original

Files changed

• crates/core/src/lib.rs — is_auto_poke field on Message, auto_poke() constructor
• crates/tui/src/app.rs — guardrail/error fields, check_auto_poke() rewrite, /poke command
• crates/cli/src/main.rs — direct model submission path
• crates/tui/src/messages/mod.rs — auto-poke color constants, conditional rendering
• crates/tools/src/todo_write.rs — is_non_retryable_error(), is_guardrail_error(), shorter message

Testing

• cargo check --workspace clean, cargo fmt clean
• 15 session browser tests, 19 todo_write tests pass

[alecuba16]

Closing in favor of consolidated group branches. The changes from this PR have been merged into a functional group branch.