/plan context clearing suggestion should offer targeted recovery options instead of a wipe

When /plan determines the context is too large or stale, it currently suggests just clearing it

It iss too destructive, relevant implementation details, prior decisions, and constraints are silently discarded, and the resulting implementation is _consistently bad_

So instead of offering a single "clear and implement" option, /plan should present three targeted recovery paths:

• Compact and implement: summarize and compress the existing context, preserving key decisions and constraints, then proceed with implementation
• Clarify and implement: prompt the user to identify which parts of the context are still relevant before proceeding, so nothing critical is dropped silently
• Clear and implement: discard context entirely and start fresh (the current behavior, demoted to an explicit last resort)

The core issue is that the current behavior conflates "context is too large" with "context is worthless"

They are never the same thing, most sessions have accumulated meaningful signal that should survive into the next implementation attempt