Closes CODAGT-157 (in part).

The docs/tutorials/quickstart.md page currently steers new users into Coder Tasks at the end of the quickstart, including a full walkthrough of pulling the tasks-docker template from the registry and creating a Task. With Coder Tasks slated for deprecation (see #24831, also under CODAGT-157) and Coder Agents now the recommended way to interact with coding agents on a Coder deployment, this PR rewinds the quickstart back to its pre-Tasks shape and points readers at the Coder Agents docs as the next step.

Changes

• Drop the trailing ### Get Coder Tasks Running section in full (the tasks-docker registry walkthrough plus the “See Tasks in action” steps).

• Drop the Tasks row from the cooking-analogy table in Understanding Coder: 30-Second Overview and the matching Inside those Workspaces, developers can also run Tasks… clause in Putting it Together.

• Drop the optional Optionally setup a **task** running Claude Code checkbox from What You'll Build, plus the You can also get Claude Code up and running in the background! aside in the lead paragraph.

• Replace the first “What’s Next?” link (“Learn more about running Coder Tasks and our recommended Best Practices”) with a link to the Coder Agents getting-started doc:

  - - [Learn more about running Coder Tasks and our recommended Best Practices](https://coder.com/docs/ai-coder/best-practices)
  + - [Try Coder Agents](../ai-coder/agents/getting-started.md), the chat
  +   interface and API for delegating development work to coding agents in your
  +   Coder deployment.

• Switch the other two coder.com/docs/... links in the same list to in-tree relative paths so they render correctly in the docs preview.

• Delete the now-unreferenced docs/images/screenshots/quickstart-tasks-background-change.png (only used by the removed Tasks section, confirmed via grep -rln).

The Docker Containers starter-template flow that the rest of the page already follows is unchanged; the user instruction in this Linear thread was specifically to keep the original template flow and drop the Tasks epilogue.

Out of scope

• This does not touch docs/start/local-deploy.md, docs/start/first-template.md, or docs/start/first-workspace.md. Those pages already use the original Docker Containers starter and never mention Coder Tasks.
• This does not touch docs/ai-coder/index.md's ## Agents with Coder Tasks section. Renaming or removing that page belongs with the broader Coder Tasks deprecation tracked in docs(docs/ai-coder): add deprecation notice to Coder Tasks pages #24831.
• The deeper docs/ai-coder/agents/ audit (auto-archive default, missing endpoints, missing tools, etc.) is tracked separately under CODAGT-157 and will land in follow-up PRs.

Validation

• pnpm exec markdownlint-cli2 docs/tutorials/quickstart.md → 0 errors.
• bash scripts/check_emdash.sh → OK, no new emdash/endash characters.
• Pre-commit hook (make pre-commit-light) passed in 6s.
• grep -in 'task\|claude' docs/tutorials/quickstart.md → no matches after the change.
• grep -rln quickstart-tasks-background-change docs/ → no matches after deletion.
• All three relative links in the new “What’s Next?” list resolve to existing files: docs/ai-coder/agents/getting-started.md, docs/user-guides/workspace-management.md, docs/admin/monitoring/index.md.

Proof

This is a docs-only change. The visible diff for the rendered page is the
textual diff in the PR. Local markdown previews of the two regions that
changed (the lead paragraph + 30-second overview at the top, and the
What's Next? list at the bottom) are attached to the originating chat
thread.

This PR was opened by Coder Agents on @david-fraley's behalf.