refactor(process): split the process manager out of the bash executor

New process/ capability family: @deepseek-ai/dsh-process owns ctx.processes —
abstract ProcessManager.spawn(spec) over a fully-explicit ProcessSpawnSpec —
plus the shared DSH_* managed-environment and CollectedOutput vocabulary;
@deepseek-ai/dsh-process-local carries the former bash-local run.ts plumbing
(detached groups, tail-keep spill-backed output, credential scrub, kill
escalation, kill-and-join disposal) with no config of its own.

dsh-bash-local becomes a consumer: it keeps command defaulting, the fused
deadline timedOut/aborted classification, the model-friendly terminal env
(now merged through the ordinary env channel), and the [stderr]-marked
background read merge, and spawns through ctx.processes. Background-process
lifetime moves to the manager, so an executor reload no longer kills live
background work; a background spawn failure is injected once into the read
path instead of being buffered as fake stderr. dsh-bash re-exports the moved
vocabulary so bash consumers keep one import root; dsh-bash-sandbox only
redeclares the inherited inject.

Every composition loading a bash executor now loads dsh-process-local (CLI,
examples, python bundled runtime, create-sdk bash feature, inline test
configs).

packages/README.md

@@ -11,6 +11,7 @@ Packages live at `packages/<group>/<pkg>/`; groups are containers, while names r
 | [`core/`](core/README.md) | Product API spine: sessions, prompts, tools, agent services, and the concrete loop | Product — stable surface |
 | [`goal/`](goal/README.md) | Persisted same-session goal state and lifecycle | Product — stable surface |
 | [`llm/`](llm/README.md) | LLM capability family: the abstract service + provider adapters | Product — stable surface |
+| [`process/`](process/README.md) | Child-process manager capability family: spawn seam + local process-group implementation | Product — stable surface |
 | [`bash/`](bash/README.md) | Bash capability family: executor seam, local impl, model-facing tool | Product — stable surface |
 | [`pty/`](pty/README.md) | Persistent PTY capability family: owner-scoped sessions, local implementation, and model-facing tools | Product — stable surface |
 | [`code-runtime/`](code-runtime/README.md) | Code-execution capability family: the runtime seam for model-written programs + a worker-thread backend | Product — stable surface |