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/ui/viewer/hooks/useTheme.ts

@@ -16,8 +16,8 @@ function getStoredPreference(): ThemePreference {
     if (stored === 'system' || stored === 'light' || stored === 'dark') {
       return stored;
     }
-  } catch (e) {
-    console.warn('Failed to read theme preference from localStorage:', e);
+  } catch (e: unknown) {
+    console.warn('Failed to read theme preference from localStorage:', e instanceof Error ? e.message : String(e));
   }
   return 'system';
 }
@@ -61,8 +61,8 @@ export function useTheme() {
     try {
       localStorage.setItem(STORAGE_KEY, newPreference);
       setPreference(newPreference);
-    } catch (e) {
-      console.warn('Failed to save theme preference to localStorage:', e);
+    } catch (e: unknown) {
+      console.warn('Failed to save theme preference to localStorage:', e instanceof Error ? e.message : String(e));
       // Still update the theme even if localStorage fails
       setPreference(newPreference);
     }