fix(discover): ignore hook-covered Claude commands

[fengjikui]

Fixes #2648.

Summary

rtk discover now detects the configured Claude Code RTK hook and stops reporting hook-covered transcript commands as missed savings.

Root cause

Claude Code session transcripts store the original Bash command before the PreToolUse hook rewrite runs. When rtk hook claude is configured, a raw transcript command such as git status may already have executed through RTK, but discover still counted it as a missed RTK opportunity.

Fix

• Add Claude hook detection to AgentIntegrationStatus, using the same Claude config directory resolution path as session discovery.
• When the Claude hook is installed, count supported transcript commands as already covered by RTK instead of adding them to the missed-savings list.
• Keep unsupported commands visible, since those are not covered by RTK rewrite rules.

Validation

• cargo fmt --check
• cargo test discover:: -- --nocapture
• cargo check
• Manual smoke with a temporary CLAUDE_CONFIG_DIR:
  • without settings.json hook: git status appears in supported
  • with rtk hook claude: supported is empty and already_rtk increments to 1