docs: cover Canvas, Workflow, Gallery, and Model Manager features (#9196)

* docs: cover Canvas, Workflow, Gallery, and Model Manager features

- New: Canvas Workflow Integration (run workflow on raster layer)
- New: Canvas Projects (.invk save/load)
- New: Custom Node Manager (install/manage community node packs)
- New: Layer tips (canvas drag & drop targets + lock transparency)
- gallery: virtual boards (by date)
- editor-interface: workflow library tags (dynamic per-user tags)
- adding-nodes: point manual install at Custom Node Manager
- models: editable source URL, bulk delete/reidentify, missing-files filter, settings export/import
- fp8-storage: hardware support tiers (Ampere / Ada+Hopper / pre-Ampere)

* docs: address review feedback

- custom-node-manager: fix broken creating-nodes link (absolute path)
- adding-nodes: fix broken community-nodes links (absolute path),
  document Workflow Connectors (#9027) under Connecting Nodes
- concepts/models: note that HF Repo IDs can be pasted into URL field,
  remove obsolete v4.0.0 autoimport tip
- fp8-storage: surface "full precision only" warning at the top,
  remove redundant quantized-formats bullet near the bottom