KB multi-article support: CRUD articles, per-article indexing, sidebar KB mode

- Replace singleton kb_content table with kb_articles (id, title, content)
- Add article_id to kb_chunks for per-article chunk tracking
- Auto-migrate old kb_content data on startup
- KbManager: index/delete per article, search across all with article_title
- API: full CRUD on /kb/articles, keep GET /kb for agent tool
- Agent: kb_search shows article labels, kb_read concatenates all articles
- Frontend: Sidebar KB mode with article list, KbEditor for single article

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/db.rs

@@ -103,8 +103,9 @@ impl Database {
 
         // KB tables
         sqlx::query(
-            "CREATE TABLE IF NOT EXISTS kb_content (
-                id INTEGER PRIMARY KEY CHECK (id = 1),
+            "CREATE TABLE IF NOT EXISTS kb_articles (
+                id TEXT PRIMARY KEY,
+                title TEXT NOT NULL,
                 content TEXT NOT NULL DEFAULT '',
                 updated_at TEXT NOT NULL DEFAULT (datetime('now'))
             )"
@@ -112,16 +113,10 @@ impl Database {
         .execute(&self.pool)
         .await?;
 
-        // Insert default row if not exists
-        let _ = sqlx::query(
-            "INSERT OR IGNORE INTO kb_content (id, content) VALUES (1, '')"
-        )
-        .execute(&self.pool)
-        .await;
-
         sqlx::query(
             "CREATE TABLE IF NOT EXISTS kb_chunks (
                 id TEXT PRIMARY KEY,
+                article_id TEXT NOT NULL,
                 title TEXT NOT NULL DEFAULT '',
                 content TEXT NOT NULL,
                 embedding BLOB NOT NULL
@@ -130,6 +125,46 @@ impl Database {
         .execute(&self.pool)
         .await?;
 
+        // Migration: add article_id to kb_chunks if missing
+        let _ = sqlx::query(
+            "ALTER TABLE kb_chunks ADD COLUMN article_id TEXT NOT NULL DEFAULT ''"
+        )
+        .execute(&self.pool)
+        .await;
+
+        // Migrate old kb_content to kb_articles
+        let has_old_table: bool = sqlx::query_scalar(
+            "SELECT COUNT(*) > 0 FROM sqlite_master WHERE type='table' AND name='kb_content'"
+        )
+        .fetch_one(&self.pool)
+        .await
+        .unwrap_or(false);
+
+        if has_old_table {
+            let old_content: Option<String> = sqlx::query_scalar(
+                "SELECT content FROM kb_content WHERE id = 1"
+            )
+            .fetch_optional(&self.pool)
+            .await
+            .unwrap_or(None);
+
+            if let Some(content) = old_content {
+                if !content.is_empty() {
+                    let id = uuid::Uuid::new_v4().to_string();
+                    let _ = sqlx::query(
+                        "INSERT OR IGNORE INTO kb_articles (id, title, content) VALUES (?, '导入的知识库', ?)"
+                    )
+                    .bind(&id)
+                    .bind(&content)
+                    .execute(&self.pool)
+                    .await;
+                }
+            }
+            let _ = sqlx::query("DROP TABLE kb_content")
+                .execute(&self.pool)
+                .await;
+        }
+
         sqlx::query(
             "CREATE TABLE IF NOT EXISTS timers (
                 id TEXT PRIMARY KEY,
@@ -192,6 +227,14 @@ pub struct Comment {
     pub created_at: String,
 }
 
+#[derive(Debug, Clone, Serialize, Deserialize, sqlx::FromRow)]
+pub struct KbArticle {
+    pub id: String,
+    pub title: String,
+    pub content: String,
+    pub updated_at: String,
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize, sqlx::FromRow)]
 pub struct Timer {
     pub id: String,