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/relative_hc_upload_urls.py

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+"""Make help-center upload URLs relative (strip baked-in absolute host)
+
+Revision ID: rel_hc_uploads_001
+Revises: add_hc_favicon_001
+Create Date: 2026-07-25
+
+Article images (baked into faqs.answer markdown) and, historically, some
+logo/favicon rows carried an absolute host in front of the /api/v1/uploads/
+path (e.g. http://localhost:8000/api/v1/uploads/...). That breaks the moment the
+help center is viewed from any other origin. Convert those to relative paths so
+they resolve against whichever origin serves the page. S3 URLs (no
+/api/v1/uploads/ segment) and already-relative paths 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 strip_upload_host
+
+revision = "rel_hc_uploads_001"
+down_revision = "add_hc_favicon_001"
+branch_labels = None
+depends_on = None
+
+
+def _rewrite(bind, table: str, column: str) -> None:
+    rows = bind.execute(
+        sa.text(f"SELECT id, {column} AS val FROM {table} WHERE {column} LIKE '%/api/v1/uploads/%'")
+    ).fetchall()
+    for row in rows:
+        new_val = strip_upload_host(row.val)
+        if new_val != row.val:
+            bind.execute(
+                sa.text(f"UPDATE {table} SET {column} = :val WHERE id = :id"),
+                {"val": new_val, "id": row.id},
+            )
+
+
+def upgrade() -> None:
+    bind = op.get_bind()
+    _rewrite(bind, "faqs", "answer")
+    _rewrite(bind, "help_center_settings", "logo_url")
+    _rewrite(bind, "help_center_settings", "favicon_url")
+
+
+def downgrade() -> None:
+    # Can't reliably re-absolutize (original host unknown); relative paths are correct anyway.
+    pass