fix: ignore transient 0% flashes in compaction counter

[KorenKrita]

Problem

The compaction counter produces false counts when Claude Code emits incomplete status JSON frames that briefly report used_percentage as 0%. Each 0% flash resets prevCtxPct to 0, and the next valid reading triggers a large drop detection — incrementing the compaction count even though no compaction occurred.

Fix

Ignore currentCtxPct values below 1% in detectCompaction(). Real compaction never drops the percentage that low, so any sub-1% reading is a transient glitch from an incomplete status JSON frame.

Changes:

• Added MIN_CTX_PCT = 1 constant
• Changed guard from currentCtxPct < 0 to currentCtxPct < MIN_CTX_PCT
• Updated the "starts at 0%" test to use 1% (0% is now filtered)
• Added tests for 0% and sub-1% glitch filtering

Testing

All 1306 tests pass, lint clean.