Deduplicate server JSON structs between publisher and registry (#318)

<!-- Provide a brief summary of your changes -->

## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->

The following PR eliminates duplicate struct definitions by migrating
the publisher tool to use canonical types from pkg/model, creating a
single source of truth across the codebase. The publisher tool
previously had its own copies of structs that were duplicated, ie.
ServerJSON, Package, Repository, VersionDetail, EnvironmentVariable,
RuntimeArgument and a few others which was not optimal


**Changes in the PR:**
- Refactored the structs to single canonical types located at pkg/model
- Refactor the implementation to use/build canonical structures directly
  - Remove all duplicate definitions (5 structs eliminated)
- Publisher now uses model.ServerJSON, model.Package, model.Repository,
etc.
- Renamed some of the structs to better reflect their use case, i.e.
ServerJSON instead of ServerDetail
- Fixes an issue where the Remote property was missing from the previous
publisher copy of the Server

**Benefits:**
  - Single source of truth - Schema changes in one place
  - Type safety - Compiler catches mismatches
  - Enhanced validation - Field constraints and bson tags
  - Zero breaking changes - Same CLI interface and JSON output
  - Future-proof - New canonical fields automatically available

Supersedes: #217 and #240

## How Has This Been Tested?
<!-- Have you tested this in a real application? Which scenarios were
tested? -->

Locally

## Breaking Changes
<!-- Will users need to update their code or configurations? -->
No

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [x] 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)
- [ ] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [ ] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [ ] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [ ] I have added or updated documentation as needed

## Additional context
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-->

---------

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>

internal/api/handlers/v0/auth/github_oidc.go

@@ -15,7 +15,6 @@ import (
 	v0 "github.com/modelcontextprotocol/registry/internal/api/handlers/v0"
 	"github.com/modelcontextprotocol/registry/internal/auth"
 	"github.com/modelcontextprotocol/registry/internal/config"
-	"github.com/modelcontextprotocol/registry/internal/model"
 )
 
 // GitHubOIDCTokenExchangeInput represents the input for GitHub OIDC token exchange
@@ -263,7 +262,7 @@ func (h *GitHubOIDCHandler) ExchangeToken(ctx context.Context, oidcToken string)
 
 	// Create JWT claims with GitHub OIDC info
 	jwtClaims := auth.JWTClaims{
-		AuthMethod:        model.AuthMethodGitHubOIDC,
+		AuthMethod:        auth.MethodGitHubOIDC,
 		AuthMethodSubject: claims.Subject, // e.g. "repo:octo-org/octo-repo:environment:prod"
 		Permissions:       permissions,
 	}