[Docs] Sync public guides with recent product changes

[roomote-community]

​Created by Roomote. View the task or mention @roomote for follow-up asks.

What changed

• document self-run Memory embeddings and reranking, including the multilingual bundled defaults and exact upstream model-name behavior
• clarify that self-host backups must preserve Memory's Markdown volume and index database together
• document visible saved-memory results, image-only Fast prompts, long-running Fast updates, and current cross-provider PR feedback behavior
• record current GLM 5.3 provider availability and correct the self-run inference example

Why this change was made

User-facing changes merged during the previous 24 hours had outpaced parts of the public documentation. The affected guides now match the shipped configuration and behavior rather than relying on release notes or implementation assumptions.

Impact

Users and self-hosting operators get accurate setup, recovery, model, Fast session, and pull-request feedback guidance. This is a documentation-only change with no runtime behavior change.

[roomote-community]

No code issues found. See task

_{Reviewed 0a65415}