* fix: isolate per-extension failures in register_enabled_extensions_for_agent
The per-extension loop had no error isolation: if registering one enabled
extension raised (e.g. an OSError writing a command file), the loop aborted and
the exception propagated, so every subsequent enabled extension was silently
skipped. Callers wrap the whole call in a single best-effort try/except, so the
wholesale abort surfaced as one warning while the command still exited 0 —
leaving the agent with only a prefix of its extensions.
Wrap the per-extension body in try/except: warn (naming the extension) and
continue, so one bad extension can no longer drop the others. Add a regression
test that forces the first-iterated extension to raise and asserts the rest
still register.
Closes#2950
* fix(extensions): preserve command registry when skills fail
* fix: clarify skill registration warning