docs(prompt): add core tool taxonomy

[Hmbown]

Summary

• add a compact tool-taxonomy block at the top of the active Agent-mode prompt and legacy agent.txt
• generate the expected taxonomy text from grouped core tool constants in prompts.rs
• add a prompt test so both prompt surfaces stay synchronized with the generated taxonomy

Verification

• cargo fmt --all -- --check
• git diff --check
• CARGO_TARGET_DIR=/Volumes/VIXinSSD/whalebro/codewhale-target/issue-2084 cargo test -p codewhale-tui agent_prompts_start_with_generated_tool_taxonomy

Related: #1708
Refs #2084

[gemini-code-assist]

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