docs: show README content on docs.rs (#583)

Use `#![doc = include_str!("../README.md")]` to display README as crate
documentation on docs.rs for both `rmcp` and `rmcp-macros`.

Changes to support this:
- Fix code examples to compile as doc tests (`rust,no_run`)
- Fix broken rustdoc links with explicit `crate::` paths
- Add "Structured Output" section and examples link to rmcp README
- Simplify rmcp-macros README to a summary table with doc links
- Fix grammar throughout
- Add CSS to hide GitHub badges when rendered as rustdoc

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

crates/rmcp-macros/src/lib.rs

@@ -1,3 +1,5 @@
+#![doc = include_str!("../README.md")]
+
 #[allow(unused_imports)]
 use proc_macro::TokenStream;