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/search_index.go

@@ -0,0 +1,36 @@
+package repository
+
+import (
+	"context"
+
+	"github.com/user/obsidian-mcp-server/internal/domain"
+)
+
+type SearchResult struct {
+	Path     string `json:"path"`
+	Score    float64 `json:"score"`
+	Matches  []*SearchMatch `json:"matches"`
+}
+
+type SearchMatch struct {
+	Line          int    `json:"line"`
+	Content       string `json:"content"`
+	ContextBefore string `json:"context_before"`
+	ContextAfter  string `json:"context_after"`
+}
+
+type SearchQuery struct {
+	Query         string
+	MaxResults    int
+	CaseSensitive bool
+	UseRegex      bool
+	ContextLines  int
+}
+
+type SearchIndex interface {
+	Index(ctx context.Context, note *domain.Note) error
+	Remove(ctx context.Context, path string) error
+	Search(ctx context.Context, query *SearchQuery) ([]*SearchResult, error)
+	Rebuild(ctx context.Context, notes []*domain.Note) error
+	Clear() error
+}