Big docs tidy up in preparation for launch (#364)

## Motivation and Context
Docs currently don't have very clear organisation, and don't explain
core flows.

This fixes #89 (although we still might want to push these to
`https://modelcontextprotocol.io/docs/`), based on the plan there.

One minor change from that plan is that I merged tutorials and guides,
because they ended up basically being duplicates which I thought would
be annoying for us to keep in sync. Additionally in the Diátaxis
framework, tutorials and guides are separated by whether they are
focused on acquisition of skills (e.g. in a learning environment) or
application of skills (e.g. in a work environment). I expect the
registry to be something that will be used occasionally in a work
environment, rather than a fundamental 'learnable' skill so I think it's
reasonable not to have tutorials and fold these into guides.

## How Has This Been Tested?
- Read through all these updated docs
- Unit and integration tests (that previously used examples.md and use
the schema) working
- Ran `npx markdown-link-check .` to check all the links work

## Breaking Changes
Links to old docs will break, but I don't think there are any. All
internal links have been checked and updated.

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [x] Documentation update

tests/integration/README.md

@@ -6,7 +6,7 @@ This directory contains an end-to-end test for publishing to the registry.
 
 1. **Publisher Tool**: Tests the `publisher` CLI that publishes metadata to the registry
 2. **Registry API**: Validates the `/v0/publish` and `/v0/servers/{id}` endpoints work correctly
-3. **Example Validation**: Ensures all example JSON in `docs/server-json/examples.md` is valid and can be published
+3. **Example Validation**: Ensures all example JSON in `docs/reference/server-json/generic-server-json.md` is valid and can be published
 4. **Data Consistency**: Verifies published data matches what's retrieved from the registry
 
 ## Test Flow

tests/integration/main.go

@@ -30,7 +30,7 @@ func main() {
 }
 
 func run() error {
-	examplesPath := filepath.Join("docs", "server-json", "examples.md")
+	examplesPath := filepath.Join("docs", "reference", "server-json", "generic-server-json.md")
 	examples, err := getExamples(examplesPath)
 	if err != nil {
 		log.Fatalf("failed to extract examples: %v", err)