Replace the over-engineered Mode interface/registry/detector pattern with
straightforward inline logic. There are only 2 modes (tag and agent) and
the complexity wasn't justified.
- Delete Mode interface, registry, and prepare pass-through modules
- Export prepareTagMode() and prepareAgentMode() as standalone functions
- Inline trigger checking and mode dispatch in run.ts/prepare.ts
- Change generatePrompt/createPrompt to take modeName string instead of Mode
- Remove dead code (extractGitHubContext, unused detector helpers)
- Update CLAUDE.md to reflect new architecture
7057f3318b