fix(tui): reject malformed tool arguments

[cyq1017]

Refs #2886

Problem

Tool argument repair fell back to {} for unrecoverable model output, so malformed tool arguments could continue into normal dispatch.

Change

• Return an argument repair error when raw arguments cannot be repaired into JSON.
• Preserve raw malformed arguments in the public tool-use event.
• Block execution with an invalid-input tool result and cover the flow in the tool lifecycle acceptance harness.

Verification

• cargo test -p codewhale-tui --test tool_lifecycle_acceptance --locked -- --nocapture
• cargo test -p codewhale-tui arg_repair --locked
• cargo test -p codewhale-tui final_tool_input --locked
• cargo fmt --all --check
• git diff --check HEAD~1..HEAD