docs: move Robusta Classic manual-upgrade content to bottom of upgrade page

[aantn]

The upgrade page opened with manual-upgrade guidance that only applies to
old Robusta Classic installs bundling kube-prometheus-stack. Reorganize so
the page leads with the simple Helm upgrade relevant to most users, and
move the manual-upgrade content into a clearly labeled 'Robusta Classic'
section at the bottom.

Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01JGdchjnKeMZEzceNvvC9oX

[github-actions]

✅ Docker image ready for 1535eb0 (built in 4m 0s)

• us-central1-docker.pkg.dev/robusta-development/temporary-builds/robusta-runner:1535eb0

⚠️ Warning: does not support ARM (ARM images are built on release only - not on every PR)

Use this tag to pull the image for testing.

📋 Copy commands

⚠️ Temporary images are deleted after 30 days. Copy to a permanent registry before using them:

gcloud auth configure-docker us-central1-docker.pkg.dev
docker pull us-central1-docker.pkg.dev/robusta-development/temporary-builds/robusta-runner:1535eb0
docker tag us-central1-docker.pkg.dev/robusta-development/temporary-builds/robusta-runner:1535eb0 me-west1-docker.pkg.dev/robusta-development/development/robusta-runner-dev:1535eb0
docker push me-west1-docker.pkg.dev/robusta-development/development/robusta-runner-dev:1535eb0

Patch Helm values in one line:

helm upgrade --install robusta robusta/robusta \
  --reuse-values \
  --set runner.image=me-west1-docker.pkg.dev/robusta-development/development/robusta-runner-dev:1535eb0

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 78ed16f6-ce1a-4e5c-b324-50567a93f291

📥 Commits

Reviewing files that changed from the base of the PR and between a48da06 and 3c14f10.

📒 Files selected for processing (1)

• docs/setup-robusta/upgrade.rst

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Walkthrough

The upgrade.rst documentation is reorganized: the "Does my upgrade require manual steps?" content is removed from its original position and relocated under a new dedicated "Manual Upgrade" → "Robusta Classic: Manual Upgrade" section. New sections for installing pre-releases and uninstalling Robusta are inserted before the manual upgrade content. A new step for thanos users on v0.10.27 or below is added to the manual upgrade steps. The previously trailing pre-release/uninstall block is removed.

Changes

Upgrade documentation restructuring

Layer / File(s)	Summary
Section relocation and new pre-release/uninstall/manual-upgrade sections docs/setup-robusta/upgrade.rst	Removes manual-upgrade guidance from its original position before "Simple Upgrade", adds new sections for installing pre-releases (helm upgrade --devel) and uninstalling Robusta (helm uninstall robusta), introduces "Manual Upgrade" / "Robusta Classic: Manual Upgrade" subsections with the relocated eligibility text, and removes the now-duplicate trailing pre-release/uninstall block.
Thanos migration step in manual upgrade list docs/setup-robusta/upgrade.rst	Adds step 3 to the manual upgrade procedure, directing users on Robusta v0.10.27 or below with thanos to adapt configuration per kube-prometheus-stack upgrade docs.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: relocating manual-upgrade content for Robusta Classic to the bottom of the upgrade documentation page.
Description check	✅ Passed	The description clearly explains the rationale for reorganizing the upgrade page to prioritize standard Helm upgrades over legacy Robusta Classic manual-upgrade guidance.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch claude/exciting-pascal-09mhaa

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