chore: codebase cleanup — remove dead code, consolidate imports, extract constants

- Remove 3 unused exported constants (TRIM_MESSAGES_TO, MAX_TERMINAL_COLS, MAX_TERMINAL_ROWS)
- Consolidate 8 direct util imports into barrel imports (./utils/index.js)
- Extract magic number 8191 to FILE_PEEK_BYTES constant in buffer-limits.ts
- Add explanatory comments to 9 undocumented .catch(() => {}) handlers

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

src/web/routes/ralph-routes.ts

@@ -505,7 +505,7 @@ export function registerRalphRoutes(
       settings.lastUsedCase = caseName;
       const dir = dirname(SETTINGS_PATH);
       if (!existsSync(dir)) mkdirSync(dir, { recursive: true });
-      fs.writeFile(SETTINGS_PATH, JSON.stringify(settings, null, 2)).catch(() => {});
+      fs.writeFile(SETTINGS_PATH, JSON.stringify(settings, null, 2)).catch(() => {}); // Ignore - persisting lastUsedCase is non-critical
     } catch {
       /* non-critical */
     }

src/web/schemas.ts

@@ -8,7 +8,7 @@
  */
 
 import { z } from 'zod';
-import { SAFE_PATH_PATTERN } from '../utils/regex-patterns.js';
+import { SAFE_PATH_PATTERN } from '../utils/index.js';
 
 // ========== Path Validation ==========