revert bash get()/list() removal — keep persistence-only prune

The original prune removed BashExecutor.get()/.list() too, but each is a
one-line accessor over the executor's already-tracked tasks map, and removing
them forced dsh-tool-bash's tests onto a ~35-line onTaskDone completion-tracking
harness just to replace the one-line ctx.bash.get(id) lookup. Per the AGENTS.md
"RFCs are proposals, not golden truth" principle, that disproportionate
migration cost is evidence the methods earn their keep — a test harness IS a
consumer programming against the seam.

Restore get()/list() (seam + LocalBashExecutor impl + the bash tests that used
them, dropping the doneFor/trackCompletions scaffolding). The persistence
has()/delete()/deleteStored removal stands — it had only contract-test callers
and no test-ergonomics cost. The RFC is retitled persistence-only with an
implementation note recording the bash revert.

packages/bash/bash-local/src/index.ts

@@ -176,12 +176,20 @@ export class LocalBashExecutor extends BashExecutor {
     return task
   }
 
+  get(id: string): BashTask | undefined {
+    return this.tasks.get(id)
+  }
+
   ownerOf(id: string): string | undefined {
     // Unknown id and known-but-ownerless both read as undefined — the consumer
     // treats undefined as "open" and a truly unknown id fails at readOutput/kill.
     return this.tasks.get(id)?.owner
   }
 
+  list(): BashTask[] {
+    return [...this.tasks.values()]
+  }
+
   readOutput(id: string): BashTaskRead {
     const task = this.tasks.get(id)
     if (!task) throw new Error(`unknown bash task "${id}"`)