Closes the Phase 5i implementation chain. When `views.is_default_for=<page>`
is set, opening that page with a "clean" URL (no chip params, no
?view=) auto-applies the saved filter + view_type. A "Showing default
view: <name> · clear" banner makes the swap visible and gives the user
a one-click out. Adding any chip param to the URL bypasses the default;
?nodefault=1 is the explicit opt-out for "I want the bare default tree".
New web/views.go: applyDefaultView gates on the param-cleanness check
+ Store.DefaultViewFor lookup. Resolution + view_type revalidation
mirror the slice D ?view=<uuid> path so a kanban-default opened on a
route that doesn't allow kanban falls back cleanly.
handleTree wires it into the existing slice D else-branch (no default
when ?view= is set). DefaultBanner field passes the applied view to
the template for the banner.
Test:
- TestDefaultViewAppliedOnCleanURL — seeds a tree default with
filter_json={tags:[work]} + view_type=card, then asserts: clean GET /
applies (card grid + banner with the view's name); ?tag=dev bypasses
(forest, no banner); ?nodefault=1 opt-out (forest, no banner).