chore: remove sources: from context:sync to disable Task source-cache

Task's sources: declaration cached the regeneration on the assumption
that adapter outputs depend only on .context/AGENT.md (or PROJECT.md +
.skills/). The cache occasionally skipped legitimate runs after manual
edits to root or template content not detectable from those source paths.
context-sync.sh is idempotent and cheap; running it on every invocation
is the right default. The freshness gate (git status --porcelain) is
unaffected — it always checked the actual git tree state.

Taskfile.yml

@@ -12,9 +12,6 @@ tasks:
     desc: Regenerate all harness-specific context files
     cmds:
       - bash scripts/context-sync.sh
-    sources:
-      - .context/PROJECT.md
-      - .skills/*/SKILL.md
 
   context:sync:claude:
     cmds: [bash scripts/context-sync.sh claude]