feat(agent): Gradio-powered LangGraph agent chat with streaming, tool calls, file upload, conversation persistence

- Gradio 5.50.0 ChatInterface with type='messages' streaming
- LangGraph create_react_agent with InMemorySaver checkpointer
- 4 @tool functions: search_dashboards, get_health_summary, list_environments, get_task_status
- Structured ChatMessage metadata (7 discriminator types: stream_token, tool_start/end/error, confirm_required, confirm_resolved, error)
- HITL resume via second submit() with interrupt_before/Command
- Dual-identity RBAC: service JWT + user JWT for tool calls
- File upload (10 MB limit, pdfplumber/xlsx/JSON parser)
- Conversation persistence via POST /api/agent/conversations/save
- REST API: list, history, archive conversations; multi-tab gate; LLM config
- LLM provider selection via Admin -> LLM Settings (assistant_planner_provider)
- Svelte 5 AgentChatModel with stream event queue, dedup, stream_status watcher
- MarkdownRenderer using svelte-markdown with semantic Tailwind tokens
- ToolCallCard (3 states: executing/completed/failed)
- ConversationList with search, date grouping, infinite scroll
- ConnectionIndicator with Gradio health status
- /agent route with two-column layout
- Vite proxy /api/agent/gradio -> Gradio SSE
- Fixed: not_() SQLAlchemy operator, route collision with _admin_routes
- Fixed: conversation_id -> id normalization, .pyc cache staleness
- Fixed: event.data array parsing (Gradio returns [jsonStr, null])
- Requirements pinned: gradio==5.50.0, pydantic>=2.7,<=2.12.3

backend/alembic/versions/f2b3c4d5e6f7_add_agent_conversations.py

@@ -0,0 +1,75 @@
+# #region Alembic.AddAgentConversations [C:2] [TYPE Function] [SEMANTICS alembic,migration,agent]
+# @BRIEF Add agent_conversations and agent_messages tables for Gradio Agent Chat.
+# @RELATION DEPENDS_ON -> [Models.Agent]
+"""add agent conversations
+
+Revision ID: f2b3c4d5e6f7
+Revises: f0e9d8c7b6a5
+Create Date: 2026-06-09 13:30:00.000000
+"""
+
+from typing import Sequence, Union
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = "f2b3c4d5e6f7"
+down_revision: Union[str, None] = "f0e9d8c7b6a5"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table(
+        "agent_conversations",
+        sa.Column("id", sa.String(), nullable=False),
+        sa.Column("user_id", sa.String(), nullable=False),
+        sa.Column("title", sa.String(256), nullable=False, server_default="New Conversation"),
+        sa.Column("is_archived", sa.Boolean(), nullable=False, server_default=sa.text("false")),
+        sa.Column("created_at", sa.DateTime(), server_default=sa.func.now()),
+        sa.Column("updated_at", sa.DateTime(), server_default=sa.func.now()),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index(
+        op.f("ix_agent_conversations_user_id"),
+        "agent_conversations",
+        ["user_id"],
+        unique=False,
+    )
+
+    op.create_table(
+        "agent_messages",
+        sa.Column("id", sa.String(), nullable=False),
+        sa.Column(
+            "conversation_id",
+            sa.String(),
+            sa.ForeignKey("agent_conversations.id"),
+            nullable=False,
+        ),
+        sa.Column("role", sa.String(16), nullable=False),
+        sa.Column("text", sa.Text(), nullable=True),
+        sa.Column("state", sa.String(32), nullable=True),
+        sa.Column("tool_calls", sa.JSON(), nullable=True),
+        sa.Column("attachments", sa.JSON(), nullable=True),
+        sa.Column("created_at", sa.DateTime(), server_default=sa.func.now()),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index(
+        op.f("ix_agent_messages_conversation_id"),
+        "agent_messages",
+        ["conversation_id"],
+        unique=False,
+    )
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_index(op.f("ix_agent_messages_conversation_id"), table_name="agent_messages")
+    op.drop_table("agent_messages")
+    op.drop_index(op.f("ix_agent_conversations_user_id"), table_name="agent_conversations")
+    op.drop_table("agent_conversations")
+    # ### end Alembic commands ###
+# #endregion Alembic.AddAgentConversations