feat: add planning mode — Glue-driven Q&A before complex tasks

Intent classification now 4-way: plan, agent, chat, clarify.
The SMART model decides when a task needs planning (complex/multi-step)
vs going straight to the agent (simple/clear).

Planning flow:
- Glue generates 1-5 clarifying questions with numbered options
- User answers by typing a number or free text
- Glue generates a markdown implementation plan
- User reviews: "go" to approve, "skip" to bypass, or type
  revision feedback to iterate
- Agent starts with enriched prompt containing plan + Q&A context

TUI integration:
- Purple border frame during planning/review states
- ◆ planning / ◆ review status in header
- ctrl+c cancels planning and returns to idle
- Input placeholder updates per state
- Plan revision loops back to review

10 new tests (70 total)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: halfaipg