feat(read): 已读功能 — 每账号标已读,列表默认隐藏

需求: 每个账号可标已读,已读过的文章刷新/重载后不在 24h feed 中显示。

设计:
- 新表 article_reads (user_id, article_id, read_at) 复合主键,on-delete CASCADE
- 迁移 0007_article_reads
- /me/reads/{id} POST/DELETE 标记 / 取消(幂等,PG upsert on_conflict_do_nothing)
- /me/reads GET 列出已读 IDs(默认 7 天,limit 500)
- articles.py 列表查询加 hide_read=true 参数(默认 true),用 NOT EXISTS 排除已读
- ArticleListItem / ArticleDetail schema 加 is_read 字段

前端:
- types 加 is_read + readsApi(mark/unmark/list)
- Feed 列表:
    顶部加 '隐藏已读' 开关,默认 ON
    每张卡片加 '标为已读 / 标为未读' 按钮(乐观更新,失败回滚)
    已读卡片 opacity 0.7 + 灰背景,标识弱化
- ArticleDetail 详情页操作栏加 '标为已读' 按钮(同样乐观)

backend/alembic/versions/0007_article_reads.py

@@ -0,0 +1,54 @@
+"""文章已读记录(per-user)
+
+- article_reads.user_id       BIGINT  FK users.id    ON DELETE CASCADE
+- article_reads.article_id    BIGINT  FK articles.id ON DELETE CASCADE
+- article_reads.read_at       TIMESTAMPTZ  DEFAULT now()
+- 复合主键 (user_id, article_id) — 天然幂等
+
+Revision ID: 0007
+Revises: 0006
+Create Date: 2026-06-13
+"""
+from __future__ import annotations
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "0007"
+down_revision: Union[str, None] = "0006"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "article_reads",
+        sa.Column("user_id", sa.BigInteger, nullable=False),
+        sa.Column("article_id", sa.BigInteger, nullable=False),
+        sa.Column("read_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.text("now()")),
+        sa.PrimaryKeyConstraint("user_id", "article_id", name="pk_article_reads"),
+        sa.ForeignKeyConstraint(
+            "user_id", ["users.id"], ondelete="CASCADE",
+        ),
+        sa.ForeignKeyConstraint(
+            "article_id", ["articles.id"], ondelete="CASCADE",
+        ),
+    )
+    op.create_index(
+        "ix_article_reads_user_read_at",
+        "article_reads",
+        ["user_id", "read_at"],
+    )
+    op.create_index(
+        "ix_article_reads_article",
+        "article_reads",
+        ["article_id"],
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_article_reads_article", table_name="article_reads")
+    op.drop_index("ix_article_reads_user_read_at", table_name="article_reads")
+    op.drop_table("article_reads")