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/config/buffer-limits.ts

@@ -56,11 +56,6 @@ export const TRIM_TEXT_TO = 768 * 1024; // 768KB
  */
 export const MAX_MESSAGES = 1000;
 
-/**
- * Number of messages to keep when trimming (80% of max).
- */
-export const TRIM_MESSAGES_TO = 800;
-
 // ============================================================================
 // Line Buffer Limits
 // ============================================================================
@@ -85,3 +80,14 @@ export const MAX_RESPAWN_BUFFER_SIZE = 1 * 1024 * 1024; // 1MB
  * Size to trim respawn buffer to when max is exceeded.
  */
 export const TRIM_RESPAWN_BUFFER_TO = 512 * 1024; // 512KB
+
+// ============================================================================
+// File Peek Limits
+// ============================================================================
+
+/**
+ * Maximum bytes to read when peeking at the beginning of a file.
+ * Used with `createReadStream({ end })` (inclusive) to read the first 8KB,
+ * which is enough to extract metadata from the first few JSONL lines.
+ */
+export const FILE_PEEK_BYTES = 8 * 1024 - 1; // 8KB (inclusive end offset)