feat(kanban): auto-subscribe on CLI create from --subscribe-* args or env vars

[crayfish-ai]

Problem

hermes kanban create does not auto-subscribe the creator to task notifications, while hermes kanban create in gateway does. The CLI path lacks the _infer_subscribe_from_env() fallback that the gateway path has.

Additionally, there is no way to explicitly subscribe on creation from the CLI without a separate hermes kanban notify-subscribe call.

Changes

1. _infer_subscribe_from_env() — new function that reads HERMES_NOTIFY_PLATFORM / HERMES_NOTIFY_CHAT_ID / HERMES_NOTIFY_THREAD_ID / HERMES_NOTIFY_USER_ID env vars, used as a fallback when no explicit --subscribe-* args are given.

2. --subscribe-platform, --subscribe-chat-id, --subscribe-thread-id, --subscribe-user-id — new CLI arguments on hermes kanban create for explicit subscription.

3. create_task() subscribe parameter — kanban_db.py now accepts an optional subscribe dict and atomically creates the notification subscription inside the same write transaction as the task row.

4. Env var fallback — When neither explicit args nor subscribe param is provided, the function falls back to HERMES_NOTIFY_* env vars (matching the gateway path behavior).

[crayfish-ai]

Closing this PR. The auto-subscribe feature will be submitted together with rerun_task and coder fixes as a single combined PR with 3 clean commits.