chore(PowerDisplay): drop personal superpowers planning docs from PR

Remove the three docs/superpowers/ markdown files (spec, plan, verification
checklist) that were committed earlier as personal dev notes — they're not
appropriate for the public PR. Also prune the expect.txt entries that were
only needed for those docs (agentic, followups, yuleng); threadpool, UIDs,
and Zenbook stay because they're referenced in PowerDisplay C# source.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Yu Leng (from Dev Box)

.github/actions/spell-check/expect.txt

@@ -26,7 +26,6 @@ advfirewall
 AFeature
 affordances
 AFX
-agentic
 agentskills
 AGGREGATABLE
 AHK
@@ -573,7 +572,6 @@ FOF
 FOFX
 FOLDERID
 folderpath
-followups
 FONTTYPE
 FORCEFILESYSTEM
 FORCEMINIMIZE
@@ -2153,7 +2151,6 @@ xxxxxx
 ycombinator
 yinle
 yinyue
-yuleng
 YVIRTUALSCREEN
 zamora
 Zenbook