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>

design.md

@@ -294,20 +294,20 @@ classDiagram
         -string path
         -string content
         -Frontmatter frontmatter
-        -[]WikiLink outlinks
-        -[]Tag tags
+        -WikiLink[] outlinks
+        -Tag[] tags
         -time createdAt
         -time modifiedAt
         +NewNote(path, content) Note
         +AddTag(tag) error
         +RemoveTag(tag) error
         +UpdateContent(content) error
-        +ExtractLinks() []WikiLink
+        +ExtractLinks() WikiLink[]
     }
     
     class Vault {
         -string rootPath
-        -[]Note notes
+        -Note[] notes
         -Graph graph
         -map tags
         +NewVault(path) Vault
@@ -317,7 +317,7 @@ classDiagram
     
     class Frontmatter {
         -map data
-        +Get(key) interface{}
+        +Get(key) any
         +Set(key, value) error
         +Merge(other) Frontmatter
     }
@@ -340,8 +340,8 @@ classDiagram
     class Graph {
         -map adjacencyList
         +AddEdge(from, to)
-        +GetBacklinks(path) []string
-        +GetOutlinks(path) []string
+        +GetBacklinks(path) string[]
+        +GetOutlinks(path) string[]
     }
     
     Vault "1" *-- "0..*" Note