Task: Remove the deleted project-document Skill requirement

Identity

Remove repository requirements for the deleted maintain-project-docs Skill and its task_context.py or Skill-owned validation commands.
Keep .project-docs/ as repository-local project memory and replace external ownership mechanics with self-contained Git worktree checks.

Preserve the user's pre-existing untracked task record and all unrelated worktree state.
Do not rewrite historical task records that accurately describe the workflow used at that time.
Do not change product behavior, release artifacts, schemas, mappings, or runtime code.

Removed every active startup, ownership, validation, and completion requirement tied to the deleted maintain-project-docs Skill, task_context.py, or Skill-owned validation scripts.
Replaced the external ownership/lock workflow with repository-local Git branch, worktree, status, base-commit, and overlap checks.
Kept .project-docs/ as the canonical project-memory location and preserved its task-record and Integration review boundaries.
Renamed the repository-hygiene test so it describes the project-memory invariant without naming the deleted Skill.
Removed the two exact .DS_Store residue files reported by repository hygiene checks; no unrelated source or task record was changed.

git diff --check: passed before the final task-record update.
node --run check:repo: passed, 10/10.
node --run check: passed.
node --run test:control-plane: passed.
node --run test:legacy: passed, 273/273.
node --run build: passed.
Active-reference scan confirmed remaining old command names occur only in historical task/reflection records or in explicit statements that they are not required.

None recorded; this task directly updates the repository-wide governance requested by the user.