Update Troubleshooting/Installation Page

General MR

Summary

Rewrote the Installation troubleshooting page since the old version was organized by generic categories instead of the order you'd actually hit a failure, which made it hard to find the right section mid-incident.

What I changed and why:

• Restructured the page around the actual troubleshooting flow — diagnose → identify where reconciliation failed → check common failure points → reconcile → recover — instead of the old "Quick Diagnostics / Installation-Specific Issues / Recovery Steps" grouping. Easier to follow when you're actually mid-incident.
• Added a symptom-to-check table so you can jump straight from what you're seeing (e.g. dependency ... is not ready, pods stuck Pending) to the right check, instead of reading through every section.
• Removed (flux diff helmrelease)
• Removed the hardcoded cert-manager|istio dependency check — Replaced with guidance to follow whatever dependency Flux actually reports.
• Updated the Full Reset section
• Added a Mermaid flowchart at the top showing the decision path (which resource fails first → which check to run), styled to match the color scheme already used on the Renovate and Troubleshooting Overview pages.
• Linked out to Flux's own docs instead of restating things like reconcile command flags — that's Flux's behavior to maintain, not ours, so if it changes we're not stuck with a stale page.

Relevant logs/screenshots

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Linked Issue

#3453 (closed)

Upgrade Notices

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