feat(hooks): add Whale agent support

[shayne-snap]

Summary

• Add Whale as a supported RTK agent target for rtk init --agent whale and rtk hook whale.
• Install and uninstall a managed Whale PreToolUse hook in project config or $WHALE_HOME / ~/.whale for global config.
• Track Whale hook installation in telemetry and document the new integration.

Closes #2207.

Test plan

• cargo fmt --all --check
• cargo clippy --all-targets
• cargo test
• bash scripts/check-test-presence.sh origin/develop
• Manual testing: installed/uninstalled Whale hook in temp project and temp WHALE_HOME
• Manual testing: verified rtk hook whale rewrites shell_run payloads with Whale updated_input
• Manual testing: verified real Whale exec session runs rewritten rtk git status command through the hook

[CLAassistant]

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