build: 打通 FastAPI 与 Vue 最小工程、依赖与数据库连接

后端入口、配置、Redis 与 Alembic 迁移就位；前端 Vite 工程可安装可构建。

backend/alembic/versions/hc_article_image_paths.py

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+"""Repoint baked absolute S3 article-image URLs at the delivery route
+
+Revision ID: hc_img_paths_001
+Revises: add_notif_prefs_001
+Create Date: 2026-07-28
+
+Article images used to be baked into faqs.answer as absolute S3 URLs. Those
+only ever worked while the bucket was publicly readable; on a correctly private
+bucket they 403. Article Markdown cannot hold a signed URL either, since it is
+stored permanently and signatures expire. Rewrite them to the stable
+/api/v1/help-center/images/<name> path, which is resolved per request against
+whichever storage backend is configured. Local /api/v1/uploads/ paths and
+non-S3 URLs are left untouched.
+Irreversible best-effort — downgrade is a no-op.
+"""
+from alembic import op
+import sqlalchemy as sa
+
+from app.services.help_center_images import rewrite_baked_s3_image_urls
+
+revision = "hc_img_paths_001"
+down_revision = "add_notif_prefs_001"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    bind = op.get_bind()
+    rows = bind.execute(
+        sa.text("SELECT id, answer FROM faqs WHERE answer LIKE '%amazonaws.com%'")
+    ).fetchall()
+    for row in rows:
+        new_answer = rewrite_baked_s3_image_urls(row.answer)
+        if new_answer != row.answer:
+            bind.execute(
+                sa.text("UPDATE faqs SET answer = :val WHERE id = :id"),
+                {"val": new_answer, "id": row.id},
+            )
+
+
+def downgrade() -> None:
+    # The original bucket/region are not recoverable from the rewritten path,
+    # and the new path works on every backend anyway.
+    pass