test(tui): cover unknown tool lifecycle errors

[cyq1017]

Refs #2886

Problem

#2886 tracks remaining tool lifecycle acceptance coverage after the existing happy-path harness. One uncovered case is an LLM requesting a tool that is not available.

Change

• Rename the tool lifecycle feature file so it can hold happy and non-happy paths.
• Add a Gherkin scenario for unknown tool calls.
• Assert the public running/error lifecycle events, the tool error sent back to the mocked LLM, and the final assistant output.

Verification

• cargo test -p codewhale-tui --test tool_lifecycle_acceptance --locked -- --nocapture
• cargo fmt --all --check
• git diff HEAD --check