Add Blog Posts CRUD with SQLite

- Add modernc.org/sqlite (pure Go, no CGO)
- Create models package with Post struct
- Implement SQLite connection and schema auto-creation
- Add CRUD methods to database package
- Create post handlers with JSON API
- Register API routes: GET/POST/PUT/DELETE /api/v1/posts
- Set default DBURL to file:./data.db with WAL mode

internal/models/models.go

@@ -0,0 +1,29 @@
+package models
+
+import (
+	"time"
+)
+
+type Post struct {
+	ID        int64     `json:"id"`
+	Title     string    `json:"title"`
+	Body      string    `json:"body"`
+	Author    string    `json:"author"`
+	Published bool      `json:"published"`
+	CreatedAt time.Time `json:"created_at"`
+	UpdatedAt time.Time `json:"updated_at"`
+}
+
+type CreatePostRequest struct {
+	Title     string `json:"title"`
+	Body      string `json:"body"`
+	Author    string `json:"author"`
+	Published bool   `json:"published"`
+}
+
+type UpdatePostRequest struct {
+	Title     *string `json:"title,omitempty"`
+	Body      *string `json:"body,omitempty"`
+	Author    *string `json:"author,omitempty"`
+	Published *bool   `json:"published,omitempty"`
+}