Add security hardening, Ghidra, recreate skill, checkpoints, shells, web search and themes

- Sandbox (bubblewrap) for non-admin shell/git, MCP per-user rights, hard budgets and quotas,
  login rate limiting, audit log and backups
- Ghidra headless decompilation (ARM64 natives built from source), binary_info tool,
  clean room / deep workflow per session
- Recreate skill and commands for analysing and re-building old software
- File checkpoints with rewind/restore, background shells (bash_output, kill_shell)
- web_search tool (DuckDuckGo, SearXNG, Brave, Tavily)
- In-app dialogs and toasts instead of browser dialogs
- 15 base themes (trilium-themes palettes plus Nord, VS Code, GitHub, Catppuccin, One,
  Dracula, Rose Pine, Everforest, Kanagawa) with light/dark/auto switcher and license notes

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/themes/nord-light.css

@@ -0,0 +1,40 @@
+/*
+ * Nord Light
+ * Palette: Nord by Arctic Ice Studio / nordtheme (MIT), Snow Storm as background.
+ */
+:root[data-theme="nord-light"] {
+  color-scheme: light;
+  --theme-color: #eceff4;
+
+  --bg0: #eceff4;
+  --bg1: #e5e9f0;
+  --bg2: #d8dee9;
+  --bg3: #c2c9d6;
+  --fg0: #2e3440;
+  --fg1: #3b4252;
+  --fg2: #434c5e;
+  --fg3: #4c566a;
+  --muted: #5f6b80;
+
+  --accent: #5e81ac;
+  --accent2: #b55f45;
+  --on-accent: #ffffff;
+  --red: #a9434d;
+  --green: #5f7d48;
+  --aqua: #4d8a89;
+  --blue: #5e81ac;
+  --purple: #8f6a8a;
+
+  --diff-add: rgba(95, 125, 72, 0.16);
+  --diff-del: rgba(169, 67, 77, 0.12);
+  --shadow: 0 6px 24px rgba(40, 40, 40, 0.18);
+
+  --syntax-keyword: #5e81ac;
+  --syntax-string: #5f7d48;
+  --syntax-number: #8f6a8a;
+  --syntax-comment: #7b88a1;
+  --syntax-function: #4c7a90;
+  --syntax-type: #4d8a89;
+  --syntax-variable: #3b4252;
+  --syntax-meta: #b55f45;
+}