feat(portal): M1 auth gate — signed magic-URL session + get_current_client

backend/portal_auth.py: stdlib HMAC-signed session cookie carrying the access-
token id (re-validated against the DB each request, so revoke kills live
sessions), hash_token, resolve_token, and the get_current_client dependency
(raises PortalAuthError). SECRET_KEY env (insecure dev default + warning).

routers/portal.py: /portal/enter/{token} mints the cookie -> /portal; /logout;
/access; /portal home stub. main.py registers the router + a PortalAuthError
handler (HTML access page for pages, 401 JSON for /portal/api/*).

Portal shell templates (base, access_required, overview stub), branded dark.

Verified: cookie round-trip + tamper/garbage rejection, token resolution
(valid/bad), get_current_client (valid/no-cookie/revoked) — 8/8 against a temp DB.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/main.py

@@ -66,6 +66,21 @@ app.mount("/static", StaticFiles(directory="backend/static"), name="static")
 # Use shared templates configuration with timezone filters
 from backend.templates_config import templates
 
+# Client-portal auth: an unauthenticated portal request renders the access page
+# (HTML routes) or returns 401 JSON (/portal/api/* routes). Centralized so every
+# portal route can simply Depends(get_current_client).
+from backend.portal_auth import PortalAuthError
+
+@app.exception_handler(PortalAuthError)
+async def portal_auth_handler(request: Request, exc: PortalAuthError):
+    if request.url.path.startswith("/portal/api"):
+        return JSONResponse(status_code=401, content={"detail": "Not authenticated"})
+    return templates.TemplateResponse(
+        "portal/access_required.html",
+        {"request": request, "reason": "required"},
+        status_code=401,
+    )
+
 # Add custom context processor to inject environment variable into all templates
 @app.middleware("http")
 async def add_environment_to_context(request: Request, call_next):
@@ -97,6 +112,10 @@ app.include_router(slmm.router)
 app.include_router(slm_ui.router)
 app.include_router(slm_dashboard.router)
 app.include_router(seismo_dashboard.router)
+
+# Client portal (read-only, scoped client view) — see docs/CLIENT_PORTAL.md
+from backend.routers import portal
+app.include_router(portal.router)
 app.include_router(sfm.router)
 app.include_router(modem_dashboard.router)