fix(dashboard): keep shell during menu transitions

Replace document navigation with native Streamlit state transitions, preserve dashboard contracts, and add regression plus authenticated browser evidence for Issue #9.

dashboard/common.py

@@ -4,7 +4,6 @@ import sqlite3
 from datetime import datetime
 from html import escape
 from typing import Any
-from urllib.parse import quote
 import importlib
 import inspect
 from zoneinfo import ZoneInfo
@@ -314,6 +313,9 @@ def inject_app_css() -> None:
             border-color: rgba(37, 99, 235, 0.48);
             box-shadow: 0 10px 22px rgba(15, 23, 42, 0.10);
         }
+        .st-key-dashboard_body:has(.st-key-dashboard_loading [data-testid="stAlert"]) .st-key-dashboard_content {
+            display: none;
+        }
         .jarca-card {
             border: 1px solid rgba(226, 232, 240, 0.86);
             border-radius: 22px;
@@ -355,13 +357,45 @@ def render_section_label(icon: str, label: str) -> None:
     st.markdown(f'<div class="jarca-section-label"><span>{escape(icon)}</span><span>{escape(label)}</span></div>', unsafe_allow_html=True)
 
 
-def render_sidebar_nav(pages: list[str], current_page: str) -> None:
-    items = []
-    for name in pages:
-        active = " active" if name == current_page else ""
-        href = f"?page={quote(name)}"
-        items.append(f'<a class="jarca-nav-item{active}" href="{href}" target="_self">{escape(name)}</a>')
-    st.markdown(f'<div class="jarca-nav-list">{"".join(items)}</div>', unsafe_allow_html=True)
+def validate_dashboard_page(page: str | None, pages: list[str]) -> str:
+    return page if page in pages else "요약"
+
+
+def _sync_dashboard_page_query() -> None:
+    st.query_params["page"] = st.session_state["dashboard_page"]
+
+
+def render_sidebar_nav(pages: list[str], current_page: str) -> str:
+    if "dashboard_page" not in st.session_state:
+        st.session_state["dashboard_page"] = current_page
+    return st.radio(
+        "메뉴",
+        pages,
+        key="dashboard_page",
+        label_visibility="collapsed",
+        on_change=_sync_dashboard_page_query,
+    )
+
+
+def render_dashboard_body(page: str, renderer) -> None:
+    body = st.empty()
+    body.empty()
+    try:
+        with body.container():
+            with st.container(key="dashboard_body"):
+                loading = st.empty()
+                with loading.container():
+                    with st.container(key="dashboard_loading"):
+                        st.info(f"{page} 불러오는 중…")
+                with st.container(key="dashboard_content"):
+                    renderer()
+                loading.empty()
+    except Exception:
+        body.empty()
+        with body.container():
+            st.error("페이지를 불러오지 못했습니다. 다시 시도해 주세요.")
+            if st.button("다시 시도", key=f"retry_{page}"):
+                st.rerun()
 
 
 def parse_optional_int(value: str, field_name: str) -> int | None: