Fix topology layout collapsing to a single column/line

[N34AY]

Summary

computeLayers() in topology_renderer.js tries to infer a network hierarchy by matching device role slugs against a hardcoded set of hints (router, core, access, server, etc). A single incidentally-matching role — e.g. one device with role "Server" among an otherwise unrelated set of custom role names — was enough to flip the entire graph into hint mode, even though only that one device had a real hint. Every other device fell through a single-pass neighbor-averaging loop that, lacking a resolved neighbor, defaulted to the same layer as that one hint, collapsing the whole diagram onto a single column.

Repro case: 609 devices, one of which has role "Server". That one match collapsed all 609 nodes onto a single layer (1 column) in Stencil/Card view.

Separately, the non-hint fallback path only ever BFS-explored from a single global root, dumping every other connected component (and any fully isolated device) into one shared fallback layer — the same collapse via a different path, for graphs that aren't one connected mesh (e.g. several independent switch stars plus many unwired spare devices — typical DCIM data).

Finally, Node (circle) view and Stencil (card) view share the same underlying node objects for x/y, but use completely different layout strategies (force simulation vs. hierarchical columns). Switching between them used to carry one view's computed positions over as the other's starting point — so Node View's force simulation would inherit Stencil View's collapsed single-file column as its initial shape, and stay collapsed since repulsion alone doesn't break a degenerate 1-D starting condition apart.

Changes

1. computeLayers(): only trust role hints once they cover a meaningful share of the graph (>=15%), otherwise fall back to connectivity-based layering.
2. computeLayers(): layer each connected component independently (BFS per-component, each restarting at layer 0) instead of a single global BFS run whose leftover nodes all collapse into one fallback layer.
3. switchView(): clear non-pinned node positions on every mode switch (mirrors what the existing "Reset Layout" button does), so each view always computes its own fresh layout instead of inheriting the other's.

Test plan

• Verified against a real 609-device / 189-cable topology extracted via the NetBox API: before the fix, all 609 nodes landed in 1 layer; after, they spread across 7 layers with a 420/16/21/42/53/35/22 split matching the actual cable hierarchy.
• Confirmed in a live NetBox 4.6 instance: Stencil view no longer collapses to one column, and switching to Node view no longer inherits a degenerate starting shape.