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/worktree.ts

@@ -38,8 +38,11 @@ export function detectWorktree(cwd: string): WorktreeInfo {
   let stat;
   try {
     stat = statSync(gitPath);
-  } catch {
-    // No .git at all - not a git repo
+  } catch (error: unknown) {
+    // No .git at all - not a git repo (ENOENT is expected, other errors are noteworthy)
+    if (error instanceof Error && (error as NodeJS.ErrnoException).code !== 'ENOENT') {
+      console.warn(`[worktree] Unexpected error checking .git:`, error);
+    }
     return NOT_A_WORKTREE;
   }
 
@@ -52,7 +55,8 @@ export function detectWorktree(cwd: string): WorktreeInfo {
   let content: string;
   try {
     content = readFileSync(gitPath, 'utf-8').trim();
-  } catch {
+  } catch (error: unknown) {
+    console.warn(`[worktree] Failed to read .git file:`, error instanceof Error ? error.message : String(error));
     return NOT_A_WORKTREE;
   }