Tasks: Set up dogfooding environment and demo for dependency management

[bpmct]

We have an internal demo on Thursday the 24th for Tasks where we'd like to show it working functionally with the coder/coder repo. Many customers are asking for real-world use cases of Agentic AI, so this would be an excellent opportunity to try using Tasks to do one of the following (these are inspired by issues completed by Blink or Claude Code in the past):

• resolving version/merge conflicts in a pull requests
• upgrading Terraform dependency to a new version (@sreya does this a lot)
• fixing (or attempting to fix a flake) in the Coder backlog

Ideally we can show this working for a real issue in coder/coder. Otherwise, we can at least it showing the coder/coder preview window, runs the task, etc.

Can we have this working by the internal demo on Thursday the 24th?

[bpmct]

@johnstcn a few notes here:

• Our tasks demo template automatically starts the dev server and has a preview window. I think this is a must for coder/coder too, but it is challenging
  • For starters, the authentication seems to work under our workspace proxy / wildcard URLs... Something I think we'll need to fix in coder/coder itself (or hack around for the dev script)
  • Second, we will probably want to replicate the same tmux hack to get the dev server working. It's just so valuable to have a preview URL immediately ready from the beginning. Especially to validate potentially low-quality work from an agent
• I'm really hopeful this will eventually enable us to do flows like Blink managing Tasks directly or devs kicking off a task to get to about 50-60% completion before taking over. So I think part of this will also be modifying the "system prompt" in this template, tools, and CLAUDE.md to make agents effective working with our codebase. This can be an eventual thing, but definitely something I think would be excellent to truly dogfood and operationalize

[johnstcn]

Addressed by a combination of

• chore: override codersdk.SessionTokenCookie in develop.sh coder#18991 <-- allows embedding the dev server
• feat: add preset selector in TasksPage coder#19012 <-- allows selecting a preset when creating a task

A future PR will update the main Coder dogfood template with tasks support.