feat: Implement foundation layer with domain entities and repository interfaces

- Add complete domain layer: Note, Vault, WikiLink, Tag, Frontmatter, Graph entities
- Implement repository interfaces for data access abstraction
- Create comprehensive configuration system with YAML and env support
- Add CLI entry point with signal handling and graceful shutdown
- Fix mermaid diagram syntax in design.md (array notation)
- Add CLAUDE.md for development guidance

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

Co-Authored-By: Claude <noreply@anthropic.com>

internal/repository/note_repository.go

@@ -0,0 +1,18 @@
+package repository
+
+import (
+	"context"
+
+	"github.com/user/obsidian-mcp-server/internal/domain"
+)
+
+type NoteRepository interface {
+	Get(ctx context.Context, path string) (*domain.Note, error)
+	Create(ctx context.Context, note *domain.Note) error
+	Update(ctx context.Context, note *domain.Note) error
+	Delete(ctx context.Context, path string) error
+	List(ctx context.Context, pattern string, recursive bool) ([]*domain.Note, error)
+	Exists(ctx context.Context, path string) bool
+	FindByTag(ctx context.Context, tag string) ([]*domain.Note, error)
+	FindByContent(ctx context.Context, query string) ([]*domain.Note, error)
+}