Add Phase 1 foundation: Go module, core types, DB infrastructure, config

Establish the project foundation with three packages:
- core: shared types (Header, Metadata, Value, ObjectType, UUID generation)
- db: SQLite migration framework, connection management (WAL, FK, busy
  timeout), transaction helpers (StartTX/EndTX), time conversion
- config: runtime configuration (DB path, blob store, Minio, gRPC addr)

Includes initial schema migration (001_initial.sql) with 13 tables covering
shared infrastructure, bibliographic data, and artifact repository. Full test
coverage for all packages, strict linting (.golangci.yaml), and Makefile.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/core_test.go

@@ -0,0 +1,106 @@
+package core
+
+import (
+	"sort"
+	"testing"
+	"time"
+)
+
+func TestNewUUID(t *testing.T) {
+	id1 := NewUUID()
+	id2 := NewUUID()
+	if id1 == "" {
+		t.Fatal("NewUUID returned empty string")
+	}
+	if id1 == id2 {
+		t.Fatal("NewUUID returned duplicate UUIDs")
+	}
+}
+
+func TestVal(t *testing.T) {
+	v := Val("hello")
+	if v.Contents != "hello" {
+		t.Fatalf("expected contents 'hello', got %q", v.Contents)
+	}
+	if v.Type != ValueTypeUnspecified {
+		t.Fatalf("expected type %q, got %q", ValueTypeUnspecified, v.Type)
+	}
+}
+
+func TestVals(t *testing.T) {
+	v := Vals("world")
+	if v.Contents != "world" {
+		t.Fatalf("expected contents 'world', got %q", v.Contents)
+	}
+	if v.Type != ValueTypeString {
+		t.Fatalf("expected type %q, got %q", ValueTypeString, v.Type)
+	}
+}
+
+func TestNewHeader(t *testing.T) {
+	before := time.Now().UTC().Unix()
+	h := NewHeader(ObjectTypeArtifact)
+	after := time.Now().UTC().Unix()
+
+	if h.ID == "" {
+		t.Fatal("header ID is empty")
+	}
+	if h.Type != ObjectTypeArtifact {
+		t.Fatalf("expected type %q, got %q", ObjectTypeArtifact, h.Type)
+	}
+	if h.Created < before || h.Created > after {
+		t.Fatalf("Created timestamp %d not in range [%d, %d]", h.Created, before, after)
+	}
+	if h.Modified != h.Created {
+		t.Fatalf("Modified (%d) should equal Created (%d)", h.Modified, h.Created)
+	}
+	if h.Meta == nil {
+		t.Fatal("Meta should not be nil")
+	}
+}
+
+func TestHeaderTouch(t *testing.T) {
+	h := NewHeader(ObjectTypeNode)
+	original := h.Modified
+	// Ensure at least 1 second passes for timestamp change.
+	time.Sleep(10 * time.Millisecond)
+	h.Touch()
+	if h.Modified < original {
+		t.Fatalf("Touch should not decrease Modified: was %d, now %d", original, h.Modified)
+	}
+}
+
+func TestMapFromList(t *testing.T) {
+	list := []string{"alpha", "beta", "gamma"}
+	m := MapFromList(list)
+	if len(m) != 3 {
+		t.Fatalf("expected 3 entries, got %d", len(m))
+	}
+	for _, s := range list {
+		if !m[s] {
+			t.Fatalf("expected %q in map", s)
+		}
+	}
+}
+
+func TestListFromMap(t *testing.T) {
+	m := map[string]bool{"z": true, "a": true, "m": true}
+	list := ListFromMap(m)
+	if len(list) != 3 {
+		t.Fatalf("expected 3 entries, got %d", len(list))
+	}
+	sort.Strings(list)
+	expected := []string{"a", "m", "z"}
+	for i, v := range list {
+		if v != expected[i] {
+			t.Fatalf("index %d: expected %q, got %q", i, expected[i], v)
+		}
+	}
+}
+
+func TestMapFromListEmpty(t *testing.T) {
+	m := MapFromList(nil)
+	if len(m) != 0 {
+		t.Fatalf("expected empty map, got %d entries", len(m))
+	}
+}