Add AI chat with skills management and model provider settings

- Model providers for OpenAI and Anthropic message formats (e.g. via
  Sub2API), with API keys encrypted at rest and never returned
- Skills tree with markdown editing, priorities, drafts, publishing and
  rollback; only published skills enter the chat prompt
- Chat page with tool calls over collected news and Binance USD-M
  klines, a persisted CONTEXT.md, reset, and stop-generation support
- Chat may only create skill drafts and update CONTEXT.md; publishing,
  deleting, moving and priority changes stay with the user

backend/src/alphapulse/ai/skills.py

@@ -0,0 +1,104 @@
+"""skills 树与版本的共用逻辑，供 skills 接口和 Chat 工具使用"""
+
+from dataclasses import dataclass
+
+from sqlalchemy import func, select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from alphapulse.models import SkillNode, SkillVersion
+
+
+class SkillError(Exception):
+    """可直接展示给用户（或模型）的业务错误"""
+
+
+@dataclass
+class NodeInfo:
+    node: SkillNode
+    path: str
+    published_version_no: int | None
+    latest_version_no: int | None
+
+    @property
+    def has_draft(self) -> bool:
+        # 存在比已发布版本更新的版本
+        return self.latest_version_no is not None and self.latest_version_no != self.published_version_no
+
+
+async def load_tree(session: AsyncSession) -> list[NodeInfo]:
+    """所有节点及其路径和版本状态，按父节点、sort_order 排序"""
+    nodes = (await session.scalars(select(SkillNode).order_by(SkillNode.parent_id.nulls_first(), SkillNode.sort_order, SkillNode.id))).all()
+    latest = dict((await session.execute(select(SkillVersion.skill_id, func.max(SkillVersion.version_no)).group_by(SkillVersion.skill_id))).all())
+    published = dict((await session.execute(
+        select(SkillNode.id, SkillVersion.version_no).join(SkillVersion, SkillVersion.id == SkillNode.published_version_id)
+    )).all())
+    by_id = {n.id: n for n in nodes}
+
+    def path(node: SkillNode) -> str:
+        parts = [node.name]
+        while node.parent_id is not None:
+            node = by_id[node.parent_id]
+            parts.append(node.name)
+        return "/".join(reversed(parts))
+
+    return [NodeInfo(n, path(n), published.get(n.id), latest.get(n.id)) for n in nodes]
+
+
+async def find_by_path(session: AsyncSession, path: str, kind: str | None = None) -> SkillNode:
+    path = path.strip("/")
+    for info in await load_tree(session):
+        if info.path == path and (kind is None or info.node.kind == kind):
+            return info.node
+    raise SkillError(f"找不到{'文件夹' if kind == 'folder' else 'skill'}：{path}")
+
+
+async def add_version(session: AsyncSession, skill: SkillNode, content: str, source: str, note: str) -> SkillVersion:
+    """追加一个新版本（不发布）；调用方负责 commit"""
+    if skill.kind != "skill":
+        raise SkillError("文件夹没有内容版本")
+    # 锁住 skill 行，避免并发保存得到相同的版本号
+    await session.execute(select(SkillNode.id).where(SkillNode.id == skill.id).with_for_update())
+    current = await session.scalar(select(func.max(SkillVersion.version_no)).where(SkillVersion.skill_id == skill.id))
+    version = SkillVersion(skill_id=skill.id, version_no=(current or 0) + 1, content=content, source=source, note=note)
+    session.add(version)
+    await session.flush()
+    return version
+
+
+async def create_node(session: AsyncSession, parent_id: int | None, kind: str, name: str, priority: int = 0) -> SkillNode:
+    name = name.strip()
+    if not name or "/" in name:
+        raise SkillError("名称不能为空，也不能包含 /")
+    if parent_id is not None:
+        parent = await session.get(SkillNode, parent_id)
+        if parent is None or parent.kind != "folder":
+            raise SkillError("只能在文件夹下新建")
+    same_parent = SkillNode.parent_id.is_not_distinct_from(parent_id)
+    if await session.scalar(select(SkillNode.id).where(same_parent, SkillNode.name == name)):
+        raise SkillError(f"同一文件夹下已存在：{name}")
+    last = await session.scalar(select(func.max(SkillNode.sort_order)).where(same_parent))
+    node = SkillNode(parent_id=parent_id, kind=kind, name=name, priority=priority, sort_order=(last or 0) + 1, enabled=True)
+    session.add(node)
+    await session.flush()
+    return node
+
+
+async def published_skills(session: AsyncSession) -> list[tuple[NodeInfo, str]]:
+    """进入 prompt 的 skills：已发布、已启用、所有上级文件夹也未停用；按优先级从高到低"""
+    tree = await load_tree(session)
+    by_id = {i.node.id: i.node for i in tree}
+
+    def active(node: SkillNode) -> bool:
+        while True:
+            if not node.enabled:
+                return False
+            if node.parent_id is None:
+                return True
+            node = by_id[node.parent_id]
+
+    chosen = [i for i in tree if i.node.kind == "skill" and i.node.published_version_id is not None and active(i.node)]
+    contents = dict((await session.execute(
+        select(SkillVersion.id, SkillVersion.content).where(SkillVersion.id.in_([i.node.published_version_id for i in chosen]))
+    )).all())
+    chosen.sort(key=lambda i: (-i.node.priority, i.path))
+    return [(i, contents[i.node.published_version_id]) for i in chosen]