PHLEGM v8 canonical path fix

- Logical/project/archive paths use single forward slashes only.
- Backslash is invalid in logical path text; this also makes mixed \/ forms invalid.
- Double slash is invalid in paths. The only permitted double slash form is the protocol delimiter in a URL, such as https://.
- ZIP member paths containing backslashes or duplicate slashes are rejected instead of silently normalized.
- Filesystem-native relative paths produced by the host OS are converted to canonical forward-slash form before validation/use.
- Fixed Developer CFG live-install synchronization so it no longer attempts to cast a multi-character backslash string to System.Char.
- External and embedded Install-and-Compile.ps1 bootstrap engines are byte-for-byte identical.
