feat: add flow index, level menus, hover delay

[damusix]

On a large model every pointer pass faded the whole view, and a flow was reachable only by drilling down from Context. Hover focus now applies once the pointer rests 300 ms; a DFD over 150 nodes + edges, or a Dictionary over 150 items, drops its transitions. Flows opens on the overview of every flow; the derived Context and 0 System levels get no crumb and no index row. A Home button returns to the overview from any depth. The flow index (☰ Process Flows or i) and the breadcrumb ▾ menus navigate by id path, because two flows can decompose same-named processes, and dfd= carries that path (invoicing/Submit-PCI) so reload and Back land on the same sub-DFD; bare-id links still resolve. The nav card is gone: leveling always yields one root, so it never rendered.

A flow folder describes itself in flows/<flow>/index.md frontmatter. The router folds that description into the row hash only when present, so existing models keep their digests. Regenerating the demo llm-memory-db-mssql routers also clears index.stale drift already on main.

[damusix]

Light theme, same states.