feat: add workflow discovery and execution

[shhac]

Summary

• Adds workflow command with list, preview, get, and run subcommands
• Discover workflows bookmarked or featured in a channel
• Preview trigger metadata, get workflow definitions including form fields/steps
• Trip workflow triggers programmatically

Form submission via --field (RTM WebSocket) will follow in a separate PR.

New files

• src/cli/workflow-command.ts — CLI command registration
• src/slack/workflows.ts — workflow discovery, preview, schema, and trigger APIs

Usage

# List workflows in a channel
agent-slack workflow list #channel

# Preview trigger metadata (no side effects)
agent-slack workflow preview <trigger-id>

# Get workflow schema (form fields + steps)
agent-slack workflow get <trigger-or-workflow-id>

# Trip a trigger
agent-slack workflow run <trigger-id> --channel #channel

Test plan

• Lint, fmt, typecheck clean
• Manual: trip-only verified against live workspace

[AmethystLiang]

Thx for the PR. Hopefully either one of me or @nwparker can help get it in today.

[shhac]

Looks like I pushed this with the wrong base last time 🙈 have rebased onto stablyai:main

[AmethystLiang]

I like the overall direction here. workflow list / preview / get / plain run all feel pretty useful and consistent with the rest of the CLI.

The one part I’m less sure about is form submission via --field. It feels like a meaningfully different level of surface area / maintenance burden from the rest of the PR, and I’m not sure we need to take that on in the first pass.

Would you be open to scoping this PR to:

• workflow list
• workflow preview
• workflow get
• workflow run without --field

and then doing form submission as a follow-up once we’ve had a chance to prove out exactly what we want to support there?

That feels like a very easy version to land, still adds real value, and keeps us from overcommitting on workflow-form support before we know how robust we want it to be.

[shhac]

@AmethystLiang I like your suggestion to narrow the scope of a single PR, splitting the concerns.

I'll take a look into how to split it neatly, if that's doable along the lines you're asking about.

I don't think any other slack tool I've seen has managed to successfully do the form submission style of slack workflow, so adding this functionality would give this cli a unique feature.
(One of the reasons why it is hard is probably the undocumented nature and webhook requirements which was the only way I found to do it based on my investigation)

[shhac]

@AmethystLiang have split the code
The second half is now on shhac:paul/feat-workflow-fields (I'll open the follow-up PR after this one lands)