Add a Drip subscriber, tag and workflow in one step

**Objective:** Add `{email}` to Drip as a subscriber, apply tag `{tag}` if given, and start the workflow named `{workflow-name}` if given.

**Step 1: Check whether they already exist**

Call `drip-get-subscriber` with `email` = `{email}`. If they exist, show their name, status and tags, and warn that `drip-add-subscriber` will update the existing record. If their status is unsubscribed, stop and tell the user: re-subscribing someone who opted out needs their explicit consent.

**Step 2: Resolve the workflow**

If `{workflow-name}` is given, call `drip-get-workflow` with `name` = `{workflow-name}`; if nothing matches, retry with `name.contains`. If more than one matches, list them and stop. If the match is not active, say so: starting a paused or draft workflow does nothing.

**Step 3: Confirm**

Show the plan: the subscriber to add or update, the tag, the workflow and its workflow-id. Wait for the user to say yes.

**Step 4: Write, in this order**

1. `drip-add-subscriber` with `email` = `{email}` and `tags` = `{tag}` if given. Pass first and last name only if the user supplied them.
2. `drip-get-subscriber` with `email` = `{email}` to read back the person-id. `drip-start-subscriber-workflow` needs the Drip subscriber ID, not the email.
3. If a workflow was resolved, `drip-start-subscriber-workflow` with `workflow_id` = the workflow-id and `id` = the person-id.

**Step 5: Verify and report**

Re-read the subscriber with `drip-get-subscriber` and report status, tags and what was done. Workflow membership cannot be read back; say the start call succeeded rather than claiming they are in it.

**Rules & Guidelines:**

* Call each write tool at most once, and only after the confirmation in Step 3.
* Do not call `drip-unsubscribe-subscriber`, any remove tool, or `drip-activate-workflow`. If the workflow is paused, report it and let the user decide.

**Validation:**

* If `{email}` is not a valid email address, ask for one before doing anything.
* If any write fails, stop, report the error, and do not run the later steps.