feat(saas): add knowledge base module — categories, items, versions, search, analytics

- 5 knowledge tables (categories, items, chunks, versions, usage) with pgvector + HNSW + GIN indexes
- 23+ API routes covering full CRUD, tree-structured categories, version snapshots
- Keyword-based search with ILIKE + array match (placeholder for vector search)
- Analytics endpoints: overview, trends, top-items, quality, gaps
- Markdown-aware content chunking with overlap strategy
- Worker dispatch for async embedding generation

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

crates/zclaw-saas/migrations/20260402000002_knowledge_base.sql

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+-- Migration: Knowledge Base tables with pgvector support
+-- 5 tables: knowledge_categories, knowledge_items, knowledge_chunks,
+--           knowledge_versions, knowledge_usage
+
+-- Enable pgvector extension
+CREATE EXTENSION IF NOT EXISTS vector;
+
+-- 行业分类树
+CREATE TABLE IF NOT EXISTS knowledge_categories (
+    id TEXT PRIMARY KEY,
+    name VARCHAR(100) NOT NULL,
+    description TEXT,
+    parent_id TEXT REFERENCES knowledge_categories(id),
+    icon VARCHAR(50),
+    sort_order INT DEFAULT 0,
+    created_at TIMESTAMPTZ DEFAULT NOW(),
+    updated_at TIMESTAMPTZ DEFAULT NOW(),
+    CHECK (id != parent_id)
+);
+CREATE INDEX IF NOT EXISTS idx_kc_parent ON knowledge_categories(parent_id);
+
+-- 知识条目
+CREATE TABLE IF NOT EXISTS knowledge_items (
+    id TEXT PRIMARY KEY,
+    category_id TEXT NOT NULL REFERENCES knowledge_categories(id),
+    title VARCHAR(255) NOT NULL,
+    content TEXT NOT NULL,
+    keywords TEXT[] DEFAULT '{}',
+    related_questions TEXT[] DEFAULT '{}',
+    priority INT DEFAULT 0,
+    status VARCHAR(20) DEFAULT 'active' CHECK (status IN ('active', 'archived', 'deprecated')),
+    version INT DEFAULT 1,
+    source VARCHAR(50) DEFAULT 'manual',
+    tags TEXT[] DEFAULT '{}',
+    created_by TEXT NOT NULL REFERENCES accounts(id),
+    created_at TIMESTAMPTZ DEFAULT NOW(),
+    updated_at TIMESTAMPTZ DEFAULT NOW(),
+    CHECK (length(content) <= 100000)
+);
+CREATE INDEX IF NOT EXISTS idx_ki_category ON knowledge_items(category_id);
+CREATE INDEX IF NOT EXISTS idx_ki_keywords ON knowledge_items USING GIN(keywords);
+
+-- 知识分块（RAG 检索核心）
+CREATE TABLE IF NOT EXISTS knowledge_chunks (
+    id TEXT PRIMARY KEY,
+    item_id TEXT NOT NULL REFERENCES knowledge_items(id) ON DELETE CASCADE,
+    chunk_index INT NOT NULL,
+    content TEXT NOT NULL,
+    embedding vector(1536),
+    keywords TEXT[] DEFAULT '{}',
+    created_at TIMESTAMPTZ DEFAULT NOW()
+);
+CREATE INDEX IF NOT EXISTS idx_kchunks_item ON knowledge_chunks(item_id);
+CREATE INDEX IF NOT EXISTS idx_kchunks_keywords ON knowledge_chunks USING GIN(keywords);
+
+-- 向量相似度索引（HNSW，无需预填充数据）
+-- 仅在有数据后创建此索引可提升性能，这里预创建
+CREATE INDEX IF NOT EXISTS idx_kchunks_embedding ON knowledge_chunks
+    USING hnsw (embedding vector_cosine_ops)
+    WITH (m = 16, ef_construction = 64);
+
+-- 版本快照
+CREATE TABLE IF NOT EXISTS knowledge_versions (
+    id TEXT PRIMARY KEY,
+    item_id TEXT NOT NULL REFERENCES knowledge_items(id) ON DELETE CASCADE,
+    version INT NOT NULL,
+    title VARCHAR(255) NOT NULL,
+    content TEXT NOT NULL,
+    keywords TEXT[] DEFAULT '{}',
+    related_questions TEXT[] DEFAULT '{}',
+    change_summary TEXT,
+    created_by TEXT NOT NULL REFERENCES accounts(id),
+    created_at TIMESTAMPTZ DEFAULT NOW()
+);
+CREATE INDEX IF NOT EXISTS idx_kv_item ON knowledge_versions(item_id);
+
+-- 使用追踪
+CREATE TABLE IF NOT EXISTS knowledge_usage (
+    id TEXT PRIMARY KEY,
+    item_id TEXT NOT NULL REFERENCES knowledge_items(id),
+    chunk_id TEXT REFERENCES knowledge_chunks(id),
+    session_id VARCHAR(100),
+    query_text TEXT,
+    relevance_score FLOAT,
+    was_injected BOOLEAN DEFAULT FALSE,
+    agent_feedback VARCHAR(20) CHECK (agent_feedback IN ('positive', 'negative')),
+    created_at TIMESTAMPTZ DEFAULT NOW()
+);
+CREATE INDEX IF NOT EXISTS idx_ku_item ON knowledge_usage(item_id);
+CREATE INDEX IF NOT EXISTS idx_ku_created ON knowledge_usage(created_at);
+
+-- 权限种子数据
+UPDATE roles
+SET permissions = REPLACE(
+    permissions,
+    ']',
+    ', "knowledge:read", "knowledge:write", "knowledge:admin", "knowledge:search"]'
+)
+WHERE name = 'super_admin'
+AND permissions NOT LIKE '%knowledge:read%';
+
+UPDATE roles
+SET permissions = REPLACE(
+    permissions,
+    ']',
+    ', "knowledge:read", "knowledge:write", "knowledge:search"]'
+)
+WHERE name = 'admin'
+AND permissions NOT LIKE '%knowledge:read%';