fix(skills): remove phantom resource references and fix CoC links (#447)

Remove references to non-existent resource files (references/, assets/,
scripts/, examples/) from 115 skill SKILL.md files. These sections
pointed to directories and files that were never created, causing
confusion when users install skills.

Also fix broken Code of Conduct links in issue templates to use
absolute GitHub URLs instead of relative paths that 404.

plugins/systems-programming/skills/rust-async-patterns/SKILL.md

@@ -511,9 +511,3 @@ tokio::spawn(async move {
 - **Don't spawn unboundedly** - Use semaphores for limits
 - **Don't ignore errors** - Propagate with `?` or log
 - **Don't forget Send bounds** - For spawned futures
-
-## Resources
-
-- [Tokio Tutorial](https://tokio.rs/tokio/tutorial)
-- [Async Book](https://rust-lang.github.io/async-book/)
-- [Tokio Console](https://github.com/tokio-rs/console)