chore(omo): vendor impeccable skill 4.6.0

Re-copy .opencode/skills/impeccable from upstream tag skill-v4.6.0
(8a0e198, engine 0.1.15), keep LICENSE, and re-apply the OmO path
rewrite and the critique routing line.

The documented rewrite missed the base-directory fallback in SKILL.md,
which ends at scripts rather than scripts/impeccable, so the upgrade
command now rewrites the scripts directory prefix. The skills README
also notes that the engine binary is downloaded by scripts/VERSION
rather than vendored.

.config/omo/skills/impeccable/scripts/impeccable.cmd

@@ -59,7 +59,7 @@ if errorlevel 1 goto download
 call :probe impeccable
 if not "%probe_ok%"=="1" goto download
 impeccable %*
-exit /b
+exit /b %errorlevel%
 
 :download
 rem Last resort: fetch this version's binary from the release channel into
@@ -166,7 +166,7 @@ exit /b 127
 
 :run
 "%run%" %*
-exit /b
+exit /b %errorlevel%
 
 :probe
 rem Sets probe_ok=1 when %1 answers the engine handshake: prints