feat(vault): integrate vault with memory graph for Obsidian-inspired system

- Add ExtractWikiLinks to vault/store.go for graph edges
- Add appendVaultGraph to api/pico.go for vault visualization
- Integrate vault notes as graph nodes in buildPicoMemoryGraph
- Vault notes become nodes (kind=document, group=memory)
- Wiki-links [[...]] become edges (kind=wikilink)
- Connect vault system to cockpit UI memory-graph component

Implements complete three-layer learning system:
1. Episodic: JSONL + frontmatter (Task 1-3)
2. Semantic: Vault with Obsidian-compatible markdown (Task 4-5)
3. Procedural: Tool skills ready (Task 6, 10)
4. UI: Vanilla JS sidebar with vault browser (Task 7-9)

pkg/vault/store.go

@@ -3,6 +3,7 @@ package vault
 import (
 	"os"
 	"path/filepath"
+	"regexp"
 	"gopkg.in/yaml.v3"
 
 	"github.com/sipeed/picoclaw/pkg/memory"
@@ -37,4 +38,15 @@ func (vs *VaultStore) ReadNote(name string) (map[string]interface{}, string, err
 		return nil, "", err
 	}
 	return memory.ParseFrontmatter(string(content))
+}
+
+// ExtractWikiLinks extracts [[link]] patterns from content
+func ExtractWikiLinks(content string) []string {
+	re := regexp.MustCompile(`\[\[([^\]]+)\]`)
+	matches := re.FindAllStringSubmatch(content, -1)
+	links := make([]string, 0, len(matches))
+	for _, m := range matches {
+		links = append(links, m[1])
+	}
+	return links
 }

web/backend/api/pico.go

@@ -459,6 +459,7 @@ func buildPicoMemoryGraph(sessionID string, messages []sessionChatMessage, works
 
 	appendMemoryDocumentGraph(memoryRootID, filepath.Join(workspaceDir, "memory", "MEMORY.md"), "memory", "Long-term Memory", 8, addNode, addEdge)
 	appendRecentDailyNoteGraph(memoryRootID, filepath.Join(workspaceDir, "memory"), addNode, addEdge)
+	appendVaultGraph(memoryRootID, filepath.Join(workspaceDir, "vault"), addNode, addEdge)
 	appendSessionGraph(sessionRootID, messages, addNode, addEdge)
 
 	sort.Slice(nodes, func(i, j int) bool {
@@ -771,6 +772,65 @@ func (h *Handler) handlePicoSetup(w http.ResponseWriter, r *http.Request) {
 	h.writePicoInfoResponse(w, r, cfg, &changed)
 }
 
+func appendVaultGraph(
+	rootID string,
+	vaultDir string,
+	addNode func(picoMemoryGraphNode),
+	addEdge func(picoMemoryGraphEdge),
+) {
+	// Read all .md files from vault directory
+	entries, err := os.ReadDir(vaultDir)
+	if err != nil {
+		return
+	}
+
+	for _, entry := range entries {
+		if entry.IsDir() || filepath.Ext(entry.Name()) != ".md" {
+			continue
+		}
+
+		notePath := filepath.Join(vaultDir, entry.Name())
+		data, err := os.ReadFile(notePath)
+		if err != nil {
+			continue
+		}
+
+		noteName := strings.TrimSuffix(entry.Name(), ".md")
+		noteID := "vault:" + noteName
+
+		// Parse frontmatter and content
+		fm, body := memory.ParseFrontmatter(string(data))
+
+		// Create node
+		label := noteName
+		if title, ok := fm["title"].(string); ok && title != "" {
+			label = title
+		}
+		preview := string(data)
+		if len(preview) > 200 {
+			preview = preview[:200] + "..."
+		}
+
+		addNode(picoMemoryGraphNode{
+			ID:      noteID,
+			Label:   label,
+			Kind:    "document",
+			Group:   "memory",
+			Preview: preview,
+			Weight:  3,
+		})
+		addEdge(picoMemoryGraphEdge{Source: rootID, Target: noteID, Kind: "contains"})
+
+		// Extract wiki-links and create edges
+		re := regexp.MustCompile(`\[\[([^\]]+)\]`)
+		matches := re.FindAllStringSubmatch(body, -1)
+		for _, m := range matches {
+			targetID := "vault:" + m[1]
+			addEdge(picoMemoryGraphEdge{Source: noteID, Target: targetID, Kind: "wikilink"})
+		}
+	}
+}
+
 // generateSecureToken creates a random 32-character hex string.
 func generateSecureToken() string {
 	b := make([]byte, 16)