fix: admin password permanent + Help/My Tasks content rendering

- main.py: lifespan insère toujours le hash de 'FlowDeck2026!' pour admin
- dashboard.py + my_tasks.py: content_html passe via {% block content %} (Jinja)
- Avant: content_html ignoré car base.html utilise des blocs, pas des variables
- 143 tests passent

app/main.py

@@ -31,9 +31,12 @@ async def lifespan(_app: FastAPI):
     init_db()
     init_webhook_tables()
     from app.db import get_conn
+    from app.password_utils import hash_password
+    admin_hash = hash_password("FlowDeck2026!")
     with get_conn() as conn:
         conn.execute(
-            "INSERT OR IGNORE INTO users (login, full_name, email, is_admin) VALUES ('admin', 'Admin', '', 1)"
+            "INSERT OR IGNORE INTO users (login, full_name, email, password_hash, is_admin) VALUES ('admin', 'Admin', '', ?, 1)",
+            (admin_hash,)
         )
         conn.commit()
     logger.info("FlowDeck v4.0.0 started on port %d", settings.app_port)

app/routers/dashboard.py

@@ -317,11 +317,14 @@ async def accounts_page(request: Request):
 @router.get("/help", response_class=HTMLResponse)
 async def help_page(request: Request):
     """Comprehensive help & documentation page."""
-    from jinja2 import Environment, FileSystemLoader
+    from jinja2 import Environment, FileSystemLoader, BaseLoader
     env = Environment(loader=FileSystemLoader("app/templates"))
     sidebar = _sidebar_data(request, [])
-    template = env.get_template("base.html")
-    return HTMLResponse(template.render(
+    # Render via a block-based template so content_html lands in {% block content %}
+    block_tpl = env.from_string(
+        '{% extends "base.html" %}{% block content %}{{ content_html|safe }}{% endblock %}'
+    )
+    return HTMLResponse(block_tpl.render(
         **sidebar,
         request=request,
         page_title="Help",

app/routers/my_tasks.py

@@ -104,8 +104,10 @@ async def my_tasks_dashboard(request: Request, view: str = "all", days: int = 7)
     from app.routers.dashboard import _sidebar_data
     env = Environment(loader=FileSystemLoader("app/templates"))
     sidebar = _sidebar_data(request, [])
-    template = env.get_template("base.html")
-    return template.render(
+    block_tpl = env.from_string(
+        '{% extends "base.html" %}{% block content %}{{ content_html|safe }}{% endblock %}'
+    )
+    return block_tpl.render(
         **sidebar,
         request=request,
         content_html=content_html,