fix: unified fullscreen terminal header

- Add showControls prop to TerminalComponent to optionally hide internal header
- Add reset() method to TerminalRef for external reset control
- TerminalPage now renders a unified fullscreen header bar combining:
  - Session tabs (TerminalSessionTabs)
  - Terminal controls (status dot, A-, A+, Reset, Exit Fullscreen)
- Unified header is always visible in fullscreen (no hover-to-reveal)
- TerminalComponent internal header hidden when in fullscreen mode
- Remove old CSS that hid session tabs with opacity:0 until hover

Quality gates: pytest 188 passed, frontend typecheck clean

Fixes: terminal-fullscreen-unified-header

apps/api/src/api/tool_instances.py

@@ -1303,6 +1303,7 @@ async def start_instance(
     home_dir = "/root"
     if tool_type and tool_type.definition_type == "manifest" and tool_type.manifest_id:
         from src.models.tool_definition_manifest import ToolDefinitionManifest
+
         manifest_def = await session.get(ToolDefinitionManifest, tool_type.manifest_id)
         if manifest_def:
             home_dir = get_manifest_home_dir(dict(manifest_def.manifest))