refactor: extract CSS modules for session/settings and delete styles.css (Task 2.3)

- Create InstanceList.module.css, AppShell.module.css, SettingsTabLayout.module.css
- Create CommitPanel.module.css, FileViewer.module.css
- Create page CSS files: sessions, repo-workspace, dashboard, projects,
  git-history, ssh-keys, settings
- Update components to import and use CSS modules
- Delete monolithic styles.css (2,255 lines)
- Update main.tsx to import page CSS and new modules

Quality gates: tsc (pass), eslint (pass), build (pass)
Refs: repo-restructure Task 2.3

apps/web/src/components/features/git/CommitPanel.module.css

@@ -0,0 +1,76 @@
+.commitPanel {
+  padding: 1rem;
+  border-top: 1px solid var(--border);
+  background: var(--panel);
+}
+
+.commitPanel h4 {
+  margin: 0 0 0.5rem 0;
+  font-size: 0.875rem;
+  font-weight: 600;
+}
+
+.fileList {
+  max-height: 150px;
+  overflow: auto;
+  margin-bottom: 0.75rem;
+}
+
+.fileItem {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  padding: 0.25rem 0;
+  font-size: 0.8125rem;
+}
+
+.fileStatus {
+  font-weight: bold;
+  font-size: 0.75rem;
+  width: 1rem;
+  text-align: center;
+}
+
+.fileItem.modified .fileStatus { color: #f59e0b; }
+.fileItem.added .fileStatus { color: #10b981; }
+.fileItem.deleted .fileStatus { color: #ef4444; }
+.fileItem.untracked .fileStatus { color: #6b7280; }
+
+.commitForm {
+  display: flex;
+  flex-direction: column;
+  gap: 0.5rem;
+}
+
+.commitMessageInput {
+  width: 100%;
+  padding: 0.5rem;
+  border: 1px solid var(--border);
+  border-radius: 4px;
+  background: var(--bg);
+  color: var(--ink);
+  font-family: inherit;
+  font-size: 0.875rem;
+  resize: vertical;
+}
+
+.commitButton {
+  padding: 0.5rem 1rem;
+  background: var(--primary);
+  color: white;
+  border: none;
+  border-radius: 4px;
+  cursor: pointer;
+  font-size: 0.875rem;
+  font-weight: 500;
+}
+
+.commitButton:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+}
+
+.commitError {
+  color: #ef4444;
+  font-size: 0.8125rem;
+}

apps/web/src/components/features/git/FileViewer.module.css

@@ -0,0 +1,45 @@
+.fileViewer {
+  background: var(--panel);
+  border: 1px solid var(--border);
+  border-radius: 8px;
+  overflow: hidden;
+}
+
+.fileViewerHeader {
+  padding: 0.75rem 1rem;
+  border-bottom: 1px solid var(--border);
+  background: var(--bg);
+}
+
+.fileBreadcrumbs {
+  font-size: 0.875rem;
+  font-family: monospace;
+}
+
+.breadcrumbSep {
+  color: var(--muted);
+  margin: 0 0.25rem;
+}
+
+.fileContent {
+  padding: 1rem;
+  overflow: auto;
+  max-height: calc(100vh - 200px);
+}
+
+.fileContent pre {
+  margin: 0;
+  font-family: "IBM Plex Mono", monospace;
+  font-size: 0.875rem;
+  line-height: 1.5;
+  white-space: pre-wrap;
+  word-wrap: break-word;
+}
+
+.fileViewerEmpty {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  height: 100%;
+  min-height: 300px;
+}