feat(workspace): add delete primitive (workspace-delete ability + CLI)

[chubes4]

Summary

Closes #64. Fills a gap where agents had to drop out of the workspace API to remove tracked files (the git rm / rm -rf workaround that bypassed containment, sensitive-path, allowlist, and primary-mutation gates).

New ability datamachine/workspace-delete plus a wp datamachine-code workspace delete <repo> <path> CLI subcommand. Tracked paths are removed via git rm so the deletion lands in working tree and index in one shot. Untracked paths are unlinked from disk; directories require --recursive.

What's added

• Workspace::delete_path() (inc/Workspace/Workspace.php) — sits next to git_add and reuses its existing gate ladder: traversal, sensitive-path, allowlist, primary-mutation. Detects tracked vs untracked via git ls-files --error-unmatch and dispatches to either git rm [-r] or a recursive filesystem unlink.
• Workspace::remove_directory_recursive() — private helper that walks an untracked directory deepest-first and reports every removed entry.
• datamachine/workspace-delete ability (inc/Abilities/WorkspaceAbilities.php) — input { repo, path, recursive?, allow_primary_mutation? }, output { success, name, repo, path, deleted[], was_tracked }. Description and category match the existing workspace abilities.
• wp datamachine-code workspace delete subcommand (inc/Cli/Commands/WorkspaceCommand.php) — same docblock + @subcommand shape as edit/write.

Why a single primitive

Splitting into delete-file + delete-directory doubles the surface for no gain. recursive flag covers directories and makes accidental recursive deletes opt-in (rejecting directories without recursive=true matches POSIX rm semantics).

Verification (live on intelligence-chubes4)

• Untracked file: delete homeboy@<branch> tmp.txt → unlink (1 path removed). ✓
• Tracked file: created → committed → delete → git status showed staged D entry. ✓
• Directory without --recursive → directory_requires_recursive error. ✓
• Directory with --recursive → unlink (4 paths removed) (file + nested file + subdir + dir). ✓
• Sensitive path (.env) → sensitive_path error. ✓
• Path traversal (../escape) → invalid_path error. ✓
• Absolute path (/abs/path) → invalid_path error. ✓
• Primary checkout without override → primary_mutation_not_allowed error. ✓
• Primary checkout with --allow-primary-mutation → succeeds. ✓
• Path not found → not_found (404) error. ✓

Out of scope

• No glob/pattern support — agents enumerate paths themselves. Consistent with git_add.
• No "soft delete" / trash semantics — git history is the undo path.
• No batch ability workspace-delete-many — agents can call once per path. Add later if it becomes a real need.

AI assistance

• AI assistance: Yes
• Tool(s): Claude Code (Sonnet 4.5)
• Used for: Drafting the gap issue (feat(workspace): add delete primitive (workspace-delete ability + CLI) #64), implementing the ability + CLI by mirroring git_add / workspace edit shapes, and live-smoke-testing every gate path on intelligence-chubes4. Chris reviewed the gap framing and authorized the upstream-first fix.