feat(git): add ignore and untrack paths commands

The changes introduce server-side commands to manage gitignore
 rules and to untrack paths without deleting local files.
 A new GitIgnoreKind enum and helper functions normalize targets
 and build proper ignore patterns, and UI code was wired to use
 these commands.

- add_to_gitignore command and related helpers
- untrack_paths command to remove paths from the index
- UI wiring to expose ignore and untrack actions in explorer

src/app.css

@@ -2350,8 +2350,20 @@
   .status-context-menu,
   .repo-tab-context-menu { position: fixed; }
 
+  .explorer-context-menu {
+    box-sizing: border-box;
+    width: min(240px, calc(100vw - 16px));
+    max-height: calc(100vh - 16px);
+    overflow-y: auto;
+    overflow-x: hidden;
+  }
+
   .status-context-menu {
+    box-sizing: border-box;
     width: min(280px, calc(100vw - 16px));
+    max-height: calc(100vh - 16px);
+    overflow-y: auto;
+    overflow-x: hidden;
     padding: 6px;
     border-color: color-mix(in srgb, var(--color-border) 78%, #5a8cf8);
     background:
@@ -2461,11 +2473,26 @@
   }
 
   .status-context-menu button {
+    box-sizing: border-box;
+    max-width: 100%;
     min-height: 42px;
     gap: 9px;
     padding: 6px 7px;
+    overflow: hidden;
   }
 
+  .explorer-context-menu button {
+    box-sizing: border-box;
+    max-width: 100%;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+  }
+
+  .explorer-context-menu button svg { flex: 0 0 auto; }
+  .explorer-context-menu button.ignore { color: #91b59a; }
+  .explorer-context-menu button.untrack { color: #d7ad6d; }
+
   .status-context-action-icon {
     width: 26px;
     height: 26px;
@@ -2475,17 +2502,26 @@
     color: var(--color-ink-dim);
   }
 
-  .status-context-action-copy { gap: 1px; }
+  .status-context-action-copy {
+    gap: 1px;
+    overflow: hidden;
+  }
   .status-context-action-copy strong {
+    overflow: hidden;
     color: var(--color-ink-muted);
     font-size: 11.5px;
     line-height: 1.25;
+    text-overflow: ellipsis;
+    white-space: nowrap;
   }
   .status-context-action-copy span {
+    overflow: hidden;
     color: var(--color-ink-faint);
     font-size: 9.5px;
     font-weight: 500;
     line-height: 1.25;
+    text-overflow: ellipsis;
+    white-space: nowrap;
   }
 
   .branch-context-menu button:hover:not(:disabled),
@@ -2506,8 +2542,18 @@
     color: var(--color-ink);
   }
 
+  .status-context-action-icon.ignore {
+    color: #91b59a;
+  }
+
+  .status-context-action-icon.untrack {
+    color: #d7ad6d;
+  }
+
   .branch-context-menu .menu-separator,
   .history-context-menu .menu-separator,
+  .explorer-context-menu .menu-separator,
+  .status-context-menu .menu-separator,
   .repo-tab-context-menu .menu-separator {
     height: 1px;
     margin: 4px 3px;