Document intentional error suppressions with comments (gt-zn9m)

All 156 instances of _ = error suppression in non-test code now have
explanatory comments documenting why the error is intentionally ignored.

Categories of intentional suppressions:
- non-fatal: session works without these - tmux environment setup
- non-fatal: theming failure does not affect operation - visual styling
- best-effort cleanup - defer cleanup on failure paths
- best-effort notification - mail/notifications that should not block
- best-effort interrupt - graceful shutdown attempts
- crypto/rand.Read only fails on broken system - random ID generation
- output errors non-actionable - fmt.Fprint to io.Writer

This addresses the silent failure and debugging concerns raised in the
issue by making the intentionality explicit in the code.

Generated with Claude Code https://claude.com/claude-code

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/polecat.go

@@ -957,7 +957,7 @@ func getGitState(worktreePath string) (*GitState, error) {
 		// origin/main might not exist - try origin/master
 		logCmd = exec.Command("git", "log", "origin/master..HEAD", "--oneline")
 		logCmd.Dir = worktreePath
-		output, _ = logCmd.Output() // Ignore error - might be a new repo
+		output, _ = logCmd.Output() // non-fatal: might be a new repo without remote tracking
 	}
 	if len(output) > 0 {
 		lines := splitLines(string(output))