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/bash/bash-sandbox/src/index.ts

@@ -34,7 +34,7 @@ export type Config = LocalConfig
  * mode; `result.sandbox` reports the mode and enforcement actually used.
  */
 export class SandboxBashExecutor extends LocalBashExecutor {
-  static inject = ['sandbox', 'sandboxPolicy']
+  static override inject = ['processes', 'sandbox', 'sandboxPolicy']
 
   // No own Config: the sandbox default (mode + workspaceRoot) moved to
   // ctx.sandboxPolicy, so this executor inherits LocalBashExecutor's Config
@@ -128,7 +128,7 @@ export class SandboxBashExecutor extends LocalBashExecutor {
    * Wrap one shell command via the `ctx.sandbox` provider: hand over the
    * exact `['bash', '-c', command]` argv this executor would spawn, get back
    * the confined argv, and re-assemble it into the `exec …` command string
-   * the inherited spawn path runs (the outer `bash -c` that `runBash` spawns
+   * the inherited spawn path runs (the outer `bash -c` the process manager spawns
    * `exec`s into the runner, so no extra shell lingers). Provider errors
    * (fail-closed `SANDBOX_UNAVAILABLE`) propagate to the caller unchanged.
    */