refactor(tasks): split the task registry into seam and local implementation

The tasks/ family now matches the capability-seam shape: @deepseek-ai/dsh-tasks
keeps the abstract TaskService (ctx.tasks contract, vocabulary types, snapshot
invariant companion) and the new @deepseek-ai/dsh-tasks-local carries the
process-local registry (LocalTaskService: in-memory store, settlement,
owner-cleanup effects, teardown, TASK_WAIT_TIMEOUT). Compositions and test
harnesses now load dsh-tasks-local; producers, TaskKindMap merges, and
dsh-tool-tasks keep importing the seam only.

Producer misconfiguration diagnostics name dsh-tasks-local because loading the
implementation is the fix. The registry behavior suite moves to tasks-local;
the seam keeps a stub-subclass registration test and the probe-based invariant
suite.

python/sdk-runtime/package.json

@@ -66,6 +66,7 @@
     "@deepseek-ai/dsh-subagent-subprocess": "workspace:^",
     "@deepseek-ai/dsh-system-prompt": "workspace:^",
     "@deepseek-ai/dsh-tasks": "workspace:^",
+    "@deepseek-ai/dsh-tasks-local": "workspace:^",
     "@deepseek-ai/dsh-timeout": "workspace:^",
     "@deepseek-ai/dsh-timeout-policy": "workspace:^",
     "@deepseek-ai/dsh-tool-ask-user": "workspace:^",