Mechanically migrates every `view!` call site: string literal props drop
`.to_string()`, constants, enum paths, literals, path calls and references to
a path drop their braces, and an attribute whose value is the binding of the
same name becomes a bare name. Also moves the missing-prop and single-child
panics out of the `unwrap_or_else` closures that hid them from
`#[track_caller]`, so they report the `view!` line, with a test for it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017W8YfdzDmZcR8A76jRjvZY