refactor: rename pkg/toolsets to pkg/registry with builder pattern

[SamMorrowDrums]

Summary

Refactors the pkg/toolsets package to pkg/registry with improved organization and a builder pattern API.

Changes

Package Rename

• Renamed pkg/toolsets → pkg/registry
• Updated all imports across the codebase (~45 files)

File Organization

Split the monolithic toolsets.go into focused files:

File	Purpose
registry.go	Core Registry struct, MCP method constants, ForMCPRequest optimization
builder.go	Builder pattern for constructing Registry instances
filters.go	Tool/resource/prompt filtering logic
server_tool.go	ServerTool, ToolsetMetadata, ToolsetID types
resources.go	ServerResourceTemplate type
prompts.go	ServerPrompt type
errors.go	ToolsetDoesNotExistError, ToolDoesNotExistError

Builder Pattern API

New fluent builder API for constructing registries:

registry := registry.NewBuilder().
    SetTools(tools...).
    SetResources(resources...).
    SetPrompts(prompts...).
    WithToolsets(enabledToolsets).
    WithReadOnly(true).
    WithFeatureChecker(checker).
    Build()

Lint Fix

• Renamed RegistryBuilder → Builder to avoid Go stuttering lint error (registry.RegistryBuilder)

Testing

• All existing tests pass
• script/lint passes
• go build ./... succeeds

Stack

This PR is stacked on #1602

[Copilot]

Pull request overview

This PR refactors the pkg/toolsets package to pkg/registry with improved organization and a builder pattern API. The main changes include renaming the package, splitting the monolithic toolsets.go into focused files (registry.go, builder.go, filters.go, etc.), introducing a builder pattern for constructing Registry instances, and converting ToolDependencies from a struct to an interface with a BaseDeps implementation.

Key Changes

• Package rename: pkg/toolsets → pkg/registry with ~45 file imports updated
• Builder pattern: New NewBuilder().SetTools().Build() API replacing direct NewRegistry().SetTools()
• ToolDependencies refactor: Changed from struct to interface with BaseDeps implementation for better flexibility

Reviewed changes

Copilot reviewed 56 out of 56 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
pkg/registry/registry.go	Core Registry struct, MCP constants, and main registry operations
pkg/registry/builder.go	Builder pattern implementation with fluent API
pkg/registry/filters.go	Tool/resource/prompt filtering logic extraction
pkg/registry/server_tool.go	ServerTool type (package declaration change only)
pkg/registry/resources.go	ServerResourceTemplate and related types
pkg/registry/prompts.go	ServerPrompt type definitions
pkg/registry/errors.go	Error type definitions
pkg/registry/registry_test.go	Test updates for builder pattern
pkg/github/dependencies.go	ToolDependencies struct→interface, BaseDeps implementation
pkg/github/*_test.go	Test updates to use BaseDeps
internal/ghmcp/server.go	Server setup refactoring with new builder pattern
e2e/e2e_test.go	E2E test updates for builder pattern
cmd/github-mcp-server/generate_docs.go	Documentation generation updates