refactor(ext/vault): extract vault-shell.ts + introduce VaultController ctx (Plan C Phase 4)

Introduces vault-context.ts (VaultView/HashRoute/VaultState types, the
VaultController contract, and the pure helpers escapeHtml/typeIcon/typeLabel/
getFilteredEntries). Extracts the shell concerns — render entry, lock screen,
3-column shell scaffolding, type picker panel, color-scheme apply, and the
session_expired listener — into vault-shell.ts. vault.ts now assembles the
ctx object and delegates shell rendering through it. No behavior change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

extension/src/vault/__tests__/sidebar-glyphs.test.ts

@@ -4,7 +4,7 @@ import * as path from 'path';
 
 describe('vault sidebar glyphs', () => {
   const vaultSrc = fs.readFileSync(
-    path.resolve(__dirname, '../vault.ts'),
+    path.resolve(__dirname, '../vault-shell.ts'),
     'utf-8',
   );