Fix infinite recursion in .copyEnv() on circular environment references

[Copilot]

.copyEnv() had no protection against circular environment references, causing infinite recursion and stack overflow when an environment directly or indirectly referenced itself.

Changes

• .copyEnv(): Added a visited hash environment parameter (defaulting to a fresh env) that maps each environment's address to its already-created copy. Before recursing, checks visited for a cached copy and returns it immediately if found. Stores the new (empty) copy in visited before populating it — critical for self-referential cases (e$self <- e).
• .copyUi(): Creates a single shared visited map and passes it to all .copyEnv() calls so shared environment references across UI items are tracked uniformly.

# Previously caused infinite recursion / stack overflow:
e <- new.env(parent = emptyenv())
e$self <- e        # direct self-reference
copy <- .copyEnv(e) # now returns safely

# Indirect cycles also handled:
a <- new.env(parent = emptyenv()); b <- new.env(parent = emptyenv())
a$other <- b; b$other <- a
copy_a <- .copyEnv(a) # no infinite recursion

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