Add UX enhancements: modals for env vars and instructions, global env vars, taskbar icon fix

- Fix Windows taskbar icon by loading icon.ico instead of icon.png (ICO contains
  multiple sizes native to Windows taskbar/title bar/alt-tab)
- Add "Container must be stopped to change settings" warning banner in config panel
- Move per-project Environment Variables and Claude Instructions into modal dialogs
  for more editing space, with buttons in the config panel to open them
- Move global Claude Instructions into a modal in Settings panel
- Add default global Claude instruction recommending git initialization
- Add global environment variables support (full stack: Rust model, TS types,
  container creation with merge logic where project overrides global for same key,
  fingerprinting for recreation checks, and Settings UI with modal)

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

app/src/components/projects/ClaudeInstructionsModal.tsx

@@ -0,0 +1,80 @@
+import { useState, useEffect, useRef, useCallback } from "react";
+
+interface Props {
+  instructions: string;
+  disabled: boolean;
+  onSave: (instructions: string) => Promise<void>;
+  onClose: () => void;
+}
+
+export default function ClaudeInstructionsModal({ instructions: initial, disabled, onSave, onClose }: Props) {
+  const [instructions, setInstructions] = useState(initial);
+  const overlayRef = useRef<HTMLDivElement>(null);
+  const textareaRef = useRef<HTMLTextAreaElement>(null);
+
+  useEffect(() => {
+    textareaRef.current?.focus();
+  }, []);
+
+  useEffect(() => {
+    const handleKeyDown = (e: KeyboardEvent) => {
+      if (e.key === "Escape") onClose();
+    };
+    document.addEventListener("keydown", handleKeyDown);
+    return () => document.removeEventListener("keydown", handleKeyDown);
+  }, [onClose]);
+
+  const handleOverlayClick = useCallback(
+    (e: React.MouseEvent<HTMLDivElement>) => {
+      if (e.target === overlayRef.current) onClose();
+    },
+    [onClose],
+  );
+
+  const handleBlur = async () => {
+    try { await onSave(instructions); } catch (err) {
+      console.error("Failed to update Claude instructions:", err);
+    }
+  };
+
+  return (
+    <div
+      ref={overlayRef}
+      onClick={handleOverlayClick}
+      className="fixed inset-0 bg-black/50 flex items-center justify-center z-50"
+    >
+      <div className="bg-[var(--bg-secondary)] border border-[var(--border-color)] rounded-lg p-6 w-[40rem] shadow-xl max-h-[80vh] flex flex-col">
+        <h2 className="text-lg font-semibold mb-1">Claude Instructions</h2>
+        <p className="text-xs text-[var(--text-secondary)] mb-4">
+          Per-project instructions for Claude Code (written to ~/.claude/CLAUDE.md in container)
+        </p>
+
+        {disabled && (
+          <div className="px-2 py-1.5 mb-3 bg-[var(--warning)]/15 border border-[var(--warning)]/30 rounded text-xs text-[var(--warning)]">
+            Container must be stopped to change Claude instructions.
+          </div>
+        )}
+
+        <textarea
+          ref={textareaRef}
+          value={instructions}
+          onChange={(e) => setInstructions(e.target.value)}
+          onBlur={handleBlur}
+          placeholder="Enter instructions for Claude Code in this project's container..."
+          disabled={disabled}
+          rows={14}
+          className="w-full flex-1 px-3 py-2 bg-[var(--bg-primary)] border border-[var(--border-color)] rounded text-sm text-[var(--text-primary)] focus:outline-none focus:border-[var(--accent)] disabled:opacity-50 resize-y font-mono"
+        />
+
+        <div className="flex justify-end mt-4">
+          <button
+            onClick={onClose}
+            className="px-4 py-2 text-sm text-[var(--text-secondary)] hover:text-[var(--text-primary)] transition-colors"
+          >
+            Close
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+}