Feature #138 (Phase 0): Add path safety and metadata stripping helpers

[Prem759-0]

Resolves Phase 0 of #138

This PR introduces the shared helpers required to implement pulling in-world objects into the local workspace (Phase 0).

Changes:

• Added a new path-safety module (src/shared/pathsafety.ts) with pure functions sanitiseSegment(name) and uniqueInDirectory(name, taken) to safely resolve paths across OS platforms without reserved characters, control characters, or namespace collisions.
• Created SynchService.stripEmittedMeta(content, language) which automatically trims the ScriptSync metadata block using language-specific comment prefixes (findMasterFileByMetaComment behavior).
• Exhaustive unit test coverage for pathsafety.ts testing collisions, truncations, and reserved filenames.
• Unit test coverage for stripEmittedMeta confirming metadata trimming in .lsl and .luau variants.

[Rider-Linden]

A heads up, I had some code that I was working on for this feature, but I'm going to let you take this ball and run with it.
Couple of things to watch. I just merged a PR that refactors the way file links work (#154) This fix should save you quite a bit of grief when the plugin links to the pulled files.

Also, can you please combine all the PRs in this feature into a single one. (so #153 will get tacked on the end here.)