fix: resolve all 301 error handling anti-patterns across codebase

Systematic cleanup of every error handling anti-pattern detected by the
automated scanner. 289 issues fixed via code changes, 12 approved with
specific technical justifications.

Changes across 90 files:
- GENERIC_CATCH (141): Added instanceof Error type discrimination
- LARGE_TRY_BLOCK (82): Extracted helper methods to narrow try scope to ≤10 lines
- NO_LOGGING_IN_CATCH (65): Added logger/console calls for error visibility
- CATCH_AND_CONTINUE_CRITICAL_PATH (10): Added throw/return or approved overrides
- ERROR_STRING_MATCHING (2): Approved with rationale (no typed error classes)
- ERROR_MESSAGE_GUESSING (1): Replaced chained .includes() with documented pattern array
- PROMISE_CATCH_NO_LOGGING (1): Added logging to .catch() handler

Also fixes a detector bug where nested try/catch inside a catch block
corrupted brace-depth tracking, causing false positives.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/utils/agents-md-utils.ts

@@ -31,7 +31,7 @@ export function writeAgentsMd(agentsPath: string, context: string): void {
   try {
     writeFileSync(tempFile, finalContent);
     renameSync(tempFile, agentsPath);
-  } catch (error) {
-    logger.error('AGENTS_MD', 'Failed to write AGENTS.md', { agentsPath }, error as Error);
+  } catch (error: unknown) {
+    logger.error('AGENTS_MD', 'Failed to write AGENTS.md', { agentsPath }, error instanceof Error ? error : new Error(String(error)));
   }
 }