* fix(@vben-core/shared): keep filterTree from mutating the source tree
filterTree assigned the filtered child array back onto the source node, so nodes that failed
the predicate were dropped from the input tree permanently instead of only from the result.
In frontend/mixed access mode generateRoutesByFrontend filters the module-level accessRoutes
on every login and role refresh, so routes stripped for a low-privilege user stayed missing
for later sessions until a full page reload.
filterTree is now pure: matched nodes owning a child array are copied, nodes without children
are still returned by reference.
* docs(@vben-core/shared): correct filterTree reference-semantics comment
filterTree does not write its result back into the input tree, but childless
matched nodes are still returned by reference. The previous comment claimed no
source node is ever returned, which contradicted the implementation and could
mislead callers.
* fix(@vben-core/shared): preserve branch references in filterTree
filterTree copied every matched branch node, so filtering a tree where nothing
changed still returned new branch objects. The previous implementation used
Array#filter, which keeps element references, so callers could rely on
filterTree(input, () => true)[0] === input[0].
Branch nodes are now shallow-copied only when their child sequence actually
changes; unchanged nodes are returned by reference, restoring the reference
semantics callers had before. The mutation fix itself is unaffected: the
filtered child array is never assigned back onto the source node.
loseintwilight
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