docs: agent temp artifact cleanup guidance and detection (#261)

Add runbook section, root-level .gitignore patterns, and detection helper
for _encode_/_emit_/_inline_ throwaway scripts. Surface non-blocking
warnings from assess_preflight_status and gitea_lock_issue.

Closes #261

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

skills/llm-project-workflow/templates/worktree-cleanup.md

@@ -20,8 +20,6 @@ Steps:
    (removes branches/<type>-issue-<n>-<slug>; refuses if dirty; git branch -d is
    safe-delete only — fails on unmerged.)
 5. Delete the remote branch if the merge did not already remove it.
-5b. Delete any throwaway agent helpers (`_encode_*.py`, `_emit_*.py`, `_inline_*.py`)
-    left in the author worktree (see docs/llm-workflow-runbooks.md § Agent temp artifact cleanup).
 6. From the main checkout: git fetch <remote> --prune; git checkout master;
    git reset --hard <remote>/master ONLY if local master safely matches remote.
 7. Confirm main checkout clean and current (git status; 0 0 vs <remote>/master).