fix: only fall back to term elaboration for compound identifiers

The previous implementation swallowed all constant lookup errors and fell
back to term elaboration. This caused:
1. Deprecated warnings not being shown (missing checkDeprecated call)
2. Wrong error messages for unknown simple identifiers

Now only fall back to term elaboration for compound identifiers like
`foo.le` where dot notation is plausible.

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Co-Authored-By: Claude <noreply@anthropic.com>