[qorzj]

Adds /compact to manually summarize the active conversation and reduce context usage while keeping the displayed history. After compaction, the CLI waits for the next user input.

• Supports command completion, progress and completion messages, and Esc cancellation without interrupting background processes.
• Handles missing sessions, unchanged conversations, and failures; updates context usage after success.
• Documents the command in the Chinese and English READMEs and the bundled reference.

Validation: npm run check and npm test (857 passed, 2 skipped).

Closes #384