v0.0.52 — no directory grouping

Finishes applying the no legacy rule (0.0.51) to the editor fanout.

Deleted

groupManifestByDir — the rule the editor tag replaced, still running whenever a manifest arrived untagged. That's the shape the rule forbids: replaced behaviour firing on the one path nobody exercises deliberately.

An untagged manifest is now one editor. That's the "do less" net rather than the "run what we rejected" net, and it reads like the rest of the harness: a subagent is not rationed, so one big assignment is a normal outcome, not a degraded one. A Coordinator that did not divide the work has not divided it.

Falls out of it

• MAX_FILES_PER_EDITOR is gone. A per-leaf size cap only existed to chunk directory groups. Nothing mechanical assembles a leaf now, and capping a deliberate assignment would hand half a feature to an editor that can't see the other half.
• Leaf labels are the Coordinator's own names (auth, docs) instead of derived paths (src/auth/, README.md), so the roster and per-editor progress lines say what each leaf is for.
• Grouping no longer reads paths at all; dirOf survives only in the labeller.

Note for anyone tuning fanout

If you rely on wide parallel edits, the Coordinator must tag entries with editor. The prompt instructs it to, but an untagged manifest will now run as a single (unrationed) editor rather than being split for you.