Fix/simple mode submodel navigation

[ellipse2v]

When a project is loaded via the directory picker, all .md files are
opened as tabs with paths relative to the project root (e.g.
"components/database.md"). Sub-model links in the SVG carry the raw DSL
value (e.g. "./components/database.md" or "../components/database.md"),
which never matched the tab paths exactly, causing openOrSwitchToTab to
open a blank new tab instead of switching to the existing one. The blank
tab produced an empty SVG, which made svg-pan-zoom crash with a
non-finite SVGMatrix error.

Replace the single exact-path lookup with a three-stage search:

1. Exact match on the raw or ./-stripped path
2. Suffix match — handles ../ references where the tab path is rooted at
   the project directory but the DSL ref is relative to the current model
3. Basename match — fallback when there is exactly one open tab with that
   filename (safe because multi-file projects rarely reuse filenames)

When projectLoaded is true and no match is found, return early with a
console warning instead of creating a blank tab (which would crash
svg-pan-zoom on the empty SVG). The blank-tab fallback is kept only for
server-managed mode where the user may legitimately start editing a new
sub-model.

Also defer svg-pan-zoom init to requestAnimationFrame with a cancellation
guard (_panZoomRafId) to prevent initialization on detached SVG elements
during rapid tab switches. All panZoomInstance.destroy() calls are
wrapped in try/catch to silence already-destroyed errors.