Add help dialog and tooltip indicators throughout the UI

- Add circled ? help button in TopBar that opens a dialog with HOW-TO-USE.md content
- Create reusable Tooltip component with viewport-aware positioning
- Add 32 tooltip indicators across project config and settings panels
- Covers backend selection, Bedrock/Ollama/LiteLLM fields, Docker, AWS, MCP, and more

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/src/components/ui/Tooltip.tsx

@@ -0,0 +1,78 @@
+import { useState, useRef, useEffect, type ReactNode } from "react";
+
+interface TooltipProps {
+  text: string;
+  children?: ReactNode;
+}
+
+/**
+ * A small circled question-mark icon that shows a tooltip on hover.
+ * Renders inline and automatically repositions to stay within the viewport.
+ */
+export default function Tooltip({ text, children }: TooltipProps) {
+  const [visible, setVisible] = useState(false);
+  const [position, setPosition] = useState<"top" | "bottom">("top");
+  const [align, setAlign] = useState<"center" | "left" | "right">("center");
+  const triggerRef = useRef<HTMLSpanElement>(null);
+  const tooltipRef = useRef<HTMLDivElement>(null);
+
+  useEffect(() => {
+    if (!visible || !triggerRef.current || !tooltipRef.current) return;
+
+    const triggerRect = triggerRef.current.getBoundingClientRect();
+    const tooltipRect = tooltipRef.current.getBoundingClientRect();
+
+    // Decide vertical position: prefer top, fall back to bottom
+    if (triggerRect.top - tooltipRect.height - 6 < 4) {
+      setPosition("bottom");
+    } else {
+      setPosition("top");
+    }
+
+    // Decide horizontal alignment
+    const centerLeft = triggerRect.left + triggerRect.width / 2 - tooltipRect.width / 2;
+    const centerRight = centerLeft + tooltipRect.width;
+    if (centerLeft < 4) {
+      setAlign("left");
+    } else if (centerRight > window.innerWidth - 4) {
+      setAlign("right");
+    } else {
+      setAlign("center");
+    }
+  }, [visible]);
+
+  const positionClasses = position === "top" ? "bottom-full mb-1.5" : "top-full mt-1.5";
+
+  const alignClasses =
+    align === "left"
+      ? "left-0"
+      : align === "right"
+        ? "right-0"
+        : "left-1/2 -translate-x-1/2";
+
+  return (
+    <span
+      ref={triggerRef}
+      className="relative inline-flex items-center ml-1"
+      onMouseEnter={() => setVisible(true)}
+      onMouseLeave={() => setVisible(false)}
+    >
+      {children ?? (
+        <span
+          className="inline-flex items-center justify-center w-3.5 h-3.5 rounded-full border border-[var(--text-secondary)] text-[var(--text-secondary)] text-[9px] leading-none cursor-help select-none hover:border-[var(--accent)] hover:text-[var(--accent)] transition-colors"
+          aria-label="Help"
+        >
+          ?
+        </span>
+      )}
+      {visible && (
+        <div
+          ref={tooltipRef}
+          className={`absolute z-50 ${positionClasses} ${alignClasses} px-2.5 py-1.5 text-[11px] leading-snug text-[var(--text-primary)] bg-[var(--bg-tertiary)] border border-[var(--border-color)] rounded shadow-lg whitespace-normal max-w-[220px] w-max pointer-events-none`}
+        >
+          {text}
+        </div>
+      )}
+    </span>
+  );
+}