Both groups only ever act on a single managed agent's state dir, so
they belong in the `agents` namespace rather than as top-level verbs
next to `forge` / `matrix` / `wg`.
Renames `quota limit` -> `quota set`: the enclosing group already
carries the noun, so the bare verb matches the flat `set-parent` /
`set-limits` spelling without stuttering, and it removes the
`set-limits` (cpu/mem) vs `quota limit` (disk) ambiguity. Adds a
cross-pointer from `set-limits` to `agents quota`.
Handlers stay in their own modules; `run_agents` gains the reparenting
glue. Regenerates docs/tools/hivectl-cli.md.
Refs #2724
