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/tmux/tmux.go

@@ -465,7 +465,7 @@ func (t *Tmux) GetSessionInfo(name string) (*SessionInfo, error) {
 	}
 
 	windows := 0
-	_, _ = fmt.Sscanf(parts[1], "%d", &windows)
+	_, _ = fmt.Sscanf(parts[1], "%d", &windows) // non-fatal: defaults to 0 on parse error
 
 	info := &SessionInfo{
 		Name:     parts[0],